The faithful were intercepted by three attackers, who started insulting and threatening them. One of the believers, Nezir Dardagan, was punched in the face and fell to the ground, Nezavisne Novine daily reported.
According to other believers, the attackers then headed towards the mosque, shouting "Ustasha! Ustasha" and obscenities.
Doctors said Dardagan had sustained light injuries.
A Zvornik Islamic community official, Mustafa Muharemovic, said the time and mode of attack indicated that "everything was well-prepared in advance to intimidate the Muslims in Zvornik."
Until 1992, Bosnian Muslims accounted for almost 60 per cent of the town's population. The area was occupied by Serb paramilitaries in April that year, with the mass murder and persecution of Bosniaks following. It is estimated that up to 900 were killed and 40,000 driven out.