Senegalese opposition leader Abdourahim Agne has been charged with threatening state security after urging peaceful demonstrations against the president.
Mr Agne (c) has been in custody since Saturday
The authorities said a recent speech he made was an incitement to rebellion.
Mr Agne, who was arrested on Saturday, could be sentenced to five years in prison if convicted.
Meanwhile, the director of a new film examining President Abdoulaye Wade's election promises has been given permisson to leave the country.
The move comes after an earlier travel ban on director Joseph Gai Ramaka was lifted.
President Wade, an advocate of African democracy, came to power in 2000.
He was closely involved in the launch of the New Partnership for Africa's Development (Nepad), which aims to bring about economic recovery through African-led reforms and good governance.
Seydou Gueye, a spokesman for the small Reform Party which Mr Agne leads, told the AFP news agency that the charges against him were based on a speech he made in the central town of Kaolack last week.
"The country is in such a dire state politically that the people should go into the streets by the millions and demonstrate peacefully for change," he said in the speech.
Justice Minister Cheikh Tidiane Sy told Reuters news agency Mr Agne had urged people to follow the example of Ukraine, where opposition supporters went into the streets last year to overturn a fraudulent election result.
President Abdoulaye Wade is seen as an advocate of democracy
"These extremely serious remarks could disrupt public order and that is why he is today held in custody," he said.
Mr Agne's lawyer Ousmane Seye said his client had been charged under laws banning attempts to overthrow the state.
He added that the state prosecutor and the investigating judge had been "very sensitive" to his poor health and allowed him to be placed in a special section of a hospital in Dakar.