Belarusian protest organizer Maria Kolesnikova was accused of inciting people to undermine national security, officials say.
Three women led a mass opposition movement, but she is the only one not to go into exile.
Ms Kolesnikova is said to have snatched her passport when authorities tried to expel her from the country.
Over the past five Sundays, at least 100,000 people have protested what were widely seen as a rigged election.
President Alexander Lukashenko claimed a landslide victory in the August 9 poll, but a brutal crackdown on the initial protests against the result only fueled popular anger.
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Svetlana Tikhanovskaya, who opposed Lukashenko as an opposition candidate, said she won the election. Shortly after, she was forced to flee to Lithuania.
The third of the three women, Veronika Tsepkalo, also left the country.
“It was claimed that if I did not voluntarily leave the Republic of Belarus, I would be taken away anyway, alive or in pieces. There were also threats to imprison me for up to 25 years,” she said in a statement presented by her. lawyer.
The investigative committee said in a statement Wednesday that Ms. Kolesnikova had been accused Monday of calling for “actions to undermine Belarusian national security” using the media and the Internet.
Meanwhile, Ms Tikhanovskaya told the BBC that the opposition was ready to talk to Russia about their attempts to oust Lukashenko.
She said she regretted President Putin’s decision to support Lukashenko, who she said was a dictator.