Yermek Narymbaev, leader of the Arman (Dream) movement, was sentenced in June 2010 to four years in prison after he was arrested at a protest calling on President Nursultan Nazarbaev to resign.
The Kazakh Bureau for Human Rights told RFE/RL that Narymbaev would be released in 15 days.
Last week, prominent Kazakh human rights activist Yevgeny Zhovtis was granted amnesty.
The amnesties have taken place as Nazarbaev this week made an official visit to Germany, during which deals worth more than $4 billion were signed.
It was Nazarbaev's first visit to the West since clashes between security forces and oil workers in the Kazakh town of Zhanaozen left at least 16 people dead in December.