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