Activists of the opposition Tell The Truth civic movement in Belarus say their colleague, Paval Vinahradau, has been detained.
Vinahradau's wife, Svyatlana, says no reasons for her husband's arrest were given.
News of Vinahradau's arrest comes a day after the offices of the Tell The Truth campaign group in Minsk were searched by police and KGB officers.
The group's computers and other equipment were sealed and all printed materials were confiscated on September 6.
The activists say the printed materials were mainly parliamentary election campaign documents.
Parliamentary elections in Belarus are scheduled for September 23.
The Tell The Truth movement, which encourages Belarusians to speak out about social problems, was launched in 2010 by opposition politician and former Belarusian presidential candidate Uladzimer Nyaklyaeu.
Vinahradau this year served 10 days in jail
over a "toy protest" in February in which toys were set up holding signs with appeals like "Where is the freedom of the press?" and "Toys against lawlessness."
Based on reports by charter97.org and Interfax