Prominent Nigerien opposition leader Hama Amadou is facing multiple charges including being involved in an organisation seeking to overthrow a democratic regime.
Mr Amadou is being held by the authorities.
Nigerien authorities have also brought charges of “regionalist propaganda” and “speech inclined to set people against one another” against the opposition leader.
At least two people died last week during protests following the presidential election in which ruling party candidate Mohamed Bazoum was declared winner with 55.75%.
Opposition candidate Mahamane Ousmane contested the results, alleging fraud.
Mr Amadou – who had once been considered the main opposition contender to run against Mr Bazoum but was banned from running – supported Mr Ousmane in the race.
Last week, Mr Ousmane’s supporters clashed with riot police in street confrontation following the announcement.
The protesters set houses on fire, including that of Radio France Internationale (RFI) correspondent Moussa Kaka.