Opposition demonstrators had gathered in a central square in the Belarussian capital Minsk since President Alexander Lukashenko secured a third term in office last Sunday.
There were about 150 protesters in the square when more than 100 riot police arrived and loaded demonstrators onto waiting trucks early on Friday morning.
Although small in scale, this has been an unprecedented protest in authoritarian Belarus. During his 12 years in office, President Lukashenko has shown little tolerance for dissent.
An Associated Press reporter at the scene said some of the demonstrators were wrestled to the ground.
The opposition's main election candidate, Alexander Milinkevich, condemned the actions of the police.
The opposition says last Sunday's election result was rigged.