"The president has signed an amnesty for about 70 political prisoners around the country," presidential advisor Hla Maung Shwe, a senior official at the Myanmar Peace Center, told AFP.
Last week Thein Sein said there would be "no prisoners of conscience in Myanmar" during a speech in London as part of a European tour aimed at shoring up the country's international image in the wake of reforms that have swept the nation since the end of junta rule in 2011.
Hla Maung Shwe said some of those being released were ethnic minority rebels from northern Kachin state, where the government is working on brokering a crucial ceasefire deal.
He said some prisoners had already been freed.