Save Fenton Town Hall say they are protesting because the Ministry of Justice (MoJ) is selling the building.
They say a World War One memorial is at risk of being destroyed if the building is sold.
However, the government has said "a legal covenant" means any buyer would have a duty to preserve the memorial.
The group said they wanted to see the building preserved for community use and were prepared to stay there all night.
The magistrates' court, which was built in 1886 as a town hall, closed in December 2012 as part of government plans to shut 93 courts in England and Wales in a bid to save Â£41m.
The Great War Memorial, which contains 498 names of soldiers from Fenton, is built into the wall of the court.
An MoJ spokesman said: "We are aware of the issue at the court. We understand the police are in attendance and the protest will be a matter for them."

French authorities say the migrants must move to cleaner and safer shipping containers on another part of the site.
But many fear this will mean they will have to stay in France, and give up their hopes of travelling to Britain.
Overnight, riot police fired tear gas at migrants who were throwing stones at the demolition squads.
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The authorities believe some 1,000 migrants will be affected by the removal plan while aid agencies say the number of people living there is much higher.
A lot of migrants and refugees have been leaving their homes in places like Syria, Afghanistan and Africa, where there is fighting, over the last year.
Many travel great distances in search of a better life in Europe and some have ended up living in the makeshift camp in Calais hoping to make their way to the UK.
Workers in high-visibility jackets could be seen tearing down structures and dumping material in a skip as police stood by on Monday.
About 100 huts were taken down.
Earlier, Good Chance, a theatre group which works in the camp, said police were preventing protestors from entering the camp.
French officials say public areas in the camp, such as places of worship and schools, will not be affected and describe the clearance as a "humanitarian operation".
Conditions in the southern sector are filthy but many residents have told the BBC that they do not want to leave.
Some 30 campaigners have occupied a former town hall and magistrates' court in Stoke-on-Trent.
[NEXT_CONCEPT]
Demolition teams have moved in to the port of Calais in France on Tuesday to break down more shelters in the migrant camp known as the "Jungle".