Kiryl Zhyvalovych, Yauhen Naporka, Maksim Dubouski, and Andrey Vislovich were found guilty on September 30 of holding an unsanctioned picket.
The activists were arrested on September 28 after participating in a marathon in Minsk while wearing T-shirts bearing the likeness of Mikalay Statkevich, a former presidential candidate who is currently in jail.
Zhyvalovich, the only one of the four who was released the day of their detention, told RFE/RL before the subsequent hearing that he will decide himself what T-shirt to wear despite any decision by any court.
Statkevich is serving a six-year prison term for "organizing mass disturbances" following President Alyaksandr Lukashenka's reelection in December 2010, which was heavily criticized by Western observers and sparked street demonstrations on election night.
The protests were brutally suppressed by authorities.