Chaima Issa was to leave prison Friday if the public prosecutor’s office did not appeal the judge’s decision.
As a result, Chaima Issa will now not leave prison on Friday, lawyer Dalila Mssadek told reporters.
A decision will be taken to release her or keep her in prison within days, lawyers said. Issa was arrested on suspicion of conspiracy.
Issa is a prominent leader in the National Salvation Front (NSF), which is the main opposition coalition to Saied, organising protests against him since he seized additional powers in 2021 and shut down the elected parliament.
Authorities have detained more than 20 political, judicial, media and business figures with opposition ties over recent months in a crackdown, accusing them of plotting against state security.
They were detained in connection with an investigation into claims of “plotting against state security” and branded as “terrorists” by Saied.
Among those detained is Rached Ghannouchi, head of the Ennahdha party, which was the largest in parliament before Saied took control.
Earlier this week, prominent Tunisian journalist Zied el-Heni was arrested by an internal squad in plain clothes who stormed his home in a suburb of the capital Tunis, according to local media.
The main opposition parties have decried the arrests as politically motivated and rights groups have urged authorities to free those detained.
On Sunday, hundreds of supporters of the NSF rallied to demand freedom for the 20 imprisoned opponents of Saied.
The president froze parliament and sacked the government in a dramatic July 2021 move against the sole democracy to emerge from the Arab Spring uprisings.
His critics have dubbed the move a “coup” while local and international rights groups decried a “witch hunt” aimed at “repressing” dissent in the North African country.