Belarussian protest organizer Maria Kolesnikova has been accused of inciting undermining national security, officials said.
Three women have led a mass position movement, but she is the only one who does not go into exile.
Mrs Kolesnikova is said to have tore up her passport as authorities tried to deport her from the country.
In the last five Sundays, at least 100,000 people have protested over what was widely considered a rigged election.
President Alexander Lukashenko claimed an overwhelming victory in the vote on August 9, but a brutal breakdown of the first protests against the result only angered the people.
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Svetlana Tikhanovskaya, who opposed Mr Lukashenko as an opposition candidate, said she won the election. She was forced to flee to Lithuania shortly after.
The third of the three women, Veronika Tsepkalo, has also left the country.
“It was declared that if I did not voluntarily leave the Republic of Belarus, I would still be taken out, alive or in pieces. There were also threats to imprison me for up to 25 years,” she said in a statement filed by her. lawyer.
On Wednesday, the commission of inquiry said in a statement that Ms Kolesnikova on Monday had been accused of calling for “actions aimed at undermining Belarus’ national security” through the media and the internet.
Meanwhile, Ms Tikhanovskaya told the BBC that the opposition was ready to talk to Russia about their attempt to deprive Mr Lukashenko.
She said she regretted President Putin’s decision to back Mr Lukashenko, who she said was a dictator.