Officials said that Belarusian protest organizer Maria Kolenikova has been accused of inciting to undermine national security.
The three women are leading a massive opposition movement, but she is the only woman not to go into exile.
Ms Kolnikova is said to have snatched her passport when authorities tried to drive her out of the country.
For the past five Sundays, at least 100,000 people have protested what was widely seen as a rigged election.
President Alexander Lukashenko claimed a landslide victory in the August 9 poll, but a ruthless action in initial protests against the result only aroused popular anger.
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Svetlana Tikankovskaya, who stood against Mr Lukashenko as the opposition candidate, said she won the election. Shortly afterwards he was forced to flee to Lithuania.
The third of three women, Veronica Tsepalko, has also left the country.
“It was said that if I did not voluntarily leave the Republic of Belarus, I would be evicted somehow, alive or in bits. I was also threatened with imprisonment for 25 years,” she said in one of her statements Was. lawyer.
On Wednesday, the investigative committee said in a statement that Ms. Kolenikova was accused of using media and internet on Monday to call for “action aimed at reducing Belarusian national security.”
Dr. Tikhanovskaya told the BBC that Russia was ready to talk to Russia about his efforts to oust Mr Lukashenko.
She said she regrets President Putin’s decision by Mr. Lukashenko, whom she said was a dictator.