Zmitser Dashkevich told RFE/RL in the courtroom after his sentence was pronounced on April 25 that his incarceration is most likely connected with the Youth Front's anticipated presence at a commemoration of the 1986 Chornobyl disaster on April 26 and during next month's Ice Hockey World Championship in Minsk.
The Belarusian opposition has called for an international boycott of the tournament.
Dashkevich has been on parole since he was released from jail last August after serving more than 2 1/2 years for allegedly assaulting two people in December 2010. Dashkevich has called the case politically motivated.
His parole ends on April 28.
Dashkevich became the fifth opposition activist in Belarus to be incarcerated this week.