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.
One of the arrested men, Kiryl Zhyvalovich, was later released. The other three remain in custody.
All four were charged with holding an unsanctioned protest and were to be tried on September 30.
Statkevich is serving a six-year prison term for "organizing mass disturbances" following authoritarian President Alyaksandr Lukashenka's reelection in December 2010.