The three-week Between the Monuments project is researching the daily lives of Neolithic and Bronze Age residents at the Wiltshire site.
The dig is being led by The National Trust and Southampton and Leicester University archaeologists.
The National Trust said if it is a house they will have "hit the jackpot".
Spokeswoman Dr Nick Snashall said: "I could count the number of middle Neolithic houses that have been found on the fingers of one hand.
"This site dates from a time when people are just starting to build the earliest parts of Avebury's earthworks, so we could be looking at the home and workplace of the people who saw that happening."
The site being excavated is next to the West Kennet Avenue - a 1.5-mile (2.5km) prehistoric avenue of two parallel lines of stones - and was first discovered by archaeologist and businessman Alexander Keiller 80 years ago.
The team has spent three years researching his journals and drawings together with modern geophysical survey techniques to pinpoint the excavation area.
They have also discovered arrowheads, clusters of scrapers for working hide and plant materials, miniature flint saws and pottery.
Dr Snashall said: "It's quite astonishing, millions of people have visited this site over the years but few of them can have guessed what they were standing on.
"The finds have been coming up three or four at a time, in clusters. It's as if the people were sitting here working away making arrowheads, scraping skins and carrying out their daily tasks and then they just got up and walked away."

The 33-year-old freelancer has been working in the country for three years for a number of media outlets, most recently NBC News.
More than 3,330 people have died in four West African countries in what has become the world's worst outbreak.
President Barack Obama has pledged federal support to contain the spread in the US, after the first case there.
A Liberian man diagnosed in Texas on Tuesday remains in a serious condition.
The unnamed cameraman is the fourth American known to test positive for Ebola, all diagnosed in Liberia.
Three American aid workers were separately flown back to the US for treatment and they are all recovering.
The man was only hired by NBC News on Tuesday, the US broadcaster said, and he came down with symptoms - including fever and aches - the following day.
After seeking medical advice, he tested positive for the virus.
NBC News President Deborah Turness informed staff of the news in a statement.
"We are doing everything we can to get him the best care possible. He will be flown back to the United States for treatment at a medical center that is equipped to handle Ebola patients."
The rest of the NBC crew including the network's chief medical editor, Dr Nancy Snyderman, are being flown back to the US on a private charter flight and will be placed under quarantine for 21 days, Ms Turness added.
Meanwhile, as many as 100 people in Texas are being checked for exposure to Ebola, after Thomas Eric Duncan, a Liberian national, was diagnosed with the virus in Dallas.
He flew to the US two weeks ago to visit relatives.
A number of them have been ordered to stay home while they are watched for signs of the disease.
Dallas Mayor Mike Rawlings was called by Mr Obama on Thursday who promised to help with whatever was needed from federal resources to stop it spreading.
Mr Duncan was the first person diagnosed on US soil and on Thursday, Liberian officials said they would prosecute him for lying on an Ebola questionnaire form prior to leaving the country.
Deputy Information Minister Isaac Jackson said Mr Duncan had "lied under oath about his Ebola status".
He is alleged to have taken a sick relative to a clinic.
In West Africa. the outbreak has prompted dire warnings of economic collapse if infection rates continue.
There have been 7,178 confirmed cases in total, with Sierra Leone, Liberia and Guinea suffering the most.
Leading charity Save the Children has warned that Ebola was spreading at a "terrifying rate" in West Africa, with the number of new recorded cases doubling every few weeks.
It said that a rate of five new Ebola cases an hour in Sierra Leone meant healthcare demands were far outstripping supply.
At a conference in London co-hosted with Sierra Leone, the UK called for urgent decisive action from the international community.
Ebola virus: Busting the myths
Archaeologists believe they may have found the remains of a house where people who built Avebury stone circle may have lived.
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A cameraman working in Liberia has tested positive for Ebola and is to be flown home to the US for treatment.