Riad Seif has been arrested several times for dissident activity
Twelve opposition activists have gone on trial in Syria's capital, Damascus.
A local rights groups said the accused denied charges including spreading false information to weaken national morale, and joining a secret group.
The accused are linked to a pro-reform body know as the Damascus Declaration group. They were arrested in the months following a group meeting in December.
Rights groups condemned the prosecution and called for their release. The trial was adjourned until 26 August.
The Damascus Declaration, signed by a group of Syrian and Lebanese intellectuals and activists in 2005, called for relations between the two countries to be improved.
The document urged democratic reform and called for Syria to recognise Lebanon as an independent state by demarcating the border.
The National Organisation for Human Rights in Syria (NOHRS) said the 12 had appeared in court and denied all of the charges against them.
"[They] stressed that the Damascus Declaration was not an undertaking [carried out] in a secret manner and that its aim was to defend the homeland," the NOHRS said in a statement.
Among the accused are journalist Ali Abdallah and former MP Riad Seif.
The NOHRS has described Mr Seif as "one of the symbols of the Damascus Spring", the period of political dialogue after the death of former President Hafez al-Assad in 2000.
The president's successor, his son Bashar, initially tolerated the discussion groups which came into being, but a tough clampdown began in 2001.
The NOHRS says the current trial is the biggest collective prosecution of Syrian dissidents in the past seven years.