A five-member group of unidentified persons on motorcycles threw two grenade at a paddy field at Belshri under Misamari Police station at around 3.30 pm, police sources said.
The grenade went off in an unpopulated open space near the railway station, the sources said.
Another unexploded grenade was also recovered from a well in the area by the local people, the sources said.
The bikers fled towards Hugrajuli, the sources said adding, a search operation was launched to track them out.