Cozma is serving a 10-year sentence for leading thousands of coal miners from the northwestern Jiu Valley to Bucharest, where they invaded parliament, set fire to government buildings and forced Petre Roman, the prime minister, to resign.
Three people were killed in the three-day rampage.
Miners descended repeatedly on the capital after a violent revolution ended communist rule in Romania in December 1989, determined to influence post-communist political developments.
Analysts said images broadcast around the world of people being beaten on the streets slowed down Romania's efforts to transform itself into a market economy by deterring foreign investment.
Cozma's term expires in 10 months, and the prison in Bucharest where he is jailed decided late last year to grant him early release for good conduct, subject to court approval.
A spokesman for the general prosecutor's office said that prosecutors would appeal against the court's decision.
"An early release for Cozma is outrageous"
- Viorel Ene,
Miners' victims association
The leader of the Miners' Victims Association, Viorel Ene, said: "An early release for Cozma is outrageous."
Protests in 1990
Cozma was not charged in connection with the miners' riot of June 1990, when 20,000 miners came to Bucharest and crushed demonstrations against Ion Iliescu, the president, leaving six people dead and more than 100 wounded.
Iliescu denied allegations that he had summoned the miners, saying they decided to board trains to the capital to rescue the nation from "hooligans".
A criminal inquiry into the violence is still under way.