The militants hurled the grenade at a temple at Mantripukhri area on the outskirts of Imphal yesterday and in the explosion the student, identified as Kunal Sahu, was injured, the police said.
Parts of the temple was also damaged in the blast, the police said,
Sahu was taken to a nearby hospital.
No individual or group has claimed responsibility for the incident.
Local inhabitants organised sit-in protests and urged the militants not to explode bombs in crowded and residential areas, the police said.