The prosector had decided to free "46 detainees", including "left-wing lawyer Haitham Mohamedin", Tariq al-Awad, a member of Egypt's Presidential Pardon Committee, said on Twitter.
No details on the identity of the other detainees were immediately available.
Mohamedin, affiliated with the Revolutionary Socialists of Egypt, was arrested in May 2018 and accused of "belonging to a terrorist group" -- a charge repeatedly levelled at critics of all stripes.
Cairo has faced frequent criticism of its human rights record under Abdel Fattah al-Sisi, who ousted Islamist president Mohamed Morsi in 2013 and was elected president the following year.
Advocacy groups say there are currently about 60,000 political prisoners in Egypt, with many facing brutal conditions and overcrowded cells.
Since al-Sisi reactivated the dormant Presidential Pardon Committee this year, dozens of such prisoners have been released from provisional detention.
On Wednesday, Al Jazeera Mubasher, the live TV unit of the Qatar-based network Al Jazeera, said Egypt's prosecutor had decided to release Ahmed al-Najdi, one of four of its journalists held in detention in the country "without trial or charge."
Najdi's health has deteriorated since his detention in August 2020.
al-Sisi this week made his first visit to Qatar since Egypt and the gas-rich Gulf state healed a diplomatic rift in January last year.
The two countries signed a clutch of economic agreements during his trip, which came as Egypt is mired in an economic crisis.