Crepin Mboli Goumba, a lawyer and coordinator for the leading opposition forum BRDC, was arrested March 3 after he accused some magistrates of corruption and said "justice is no longer being served in the name of the people."
He was also ordered to pay a fine of 80 million CFA francs, or nearly 122,000 euros, said an AFP reporter at court.
Prosecutors had sought a one-year jail term and a 125-million CFA franc fine for Mboli Goumba, who also leads the PATRIE party.
International human rights groups regularly condemn the crackdown on all opposition forces in Central African Republic (CAR), ranked by the United Nations as one of the four least developed in the world.
Mboli Goumba, who had denounced his arrest as illegal and refused to answer prosecutors' questions, will appeal, his lawyers said, condemning a "political trial."
Opposition gatherings are nearly always banned in CAR where NGOs denounce threats and intimidation against non-government politicians.
Opposition MP Dominique Yandocka has been in detention since December 15, despite his parliamentary immunity, accused of an attempted coup. Details of the accusation have never been made public.
New York-based Human Rights Watch last year said President Faustin Archange Touadera's regime "is repressing civil society, media and opposition political parties."
Touadera won a 2016 election during a lull in a seemingly endless civil war.
Last July he pushed through a new constitution enabling him to run for a third term in office at next year's election.
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