The militants threw the grenade at the residence of executive engineer of Lokta Lake Development Authority Ashem Kumarjit yesterday at Singjamei Naorem Leikai area under Singjamei police station.
The official and his family were not present at the time.
The grenade was later defused by bomb experts.
No individual or group has claimed responsibility for the incident.
Police said they would investigate whether it was related to extortion.