The militants exploded the powerful grenade at the gate of government contractor Kh. Surjit at Ningthem Pukhri Mapal area near here last midnight when Surjit and family members were sleeping.
No casualty was reported but the explosion destroyed windows of three houses, including Surjit's, police said, adding that the attackers escaped under the cover of darkness.
The motive behind the attack was not known as family sources of the contractor said no militant outfit had demanded money from them.
No individual or group has claimed responsibility.
Police said they would investigate whether the case was connected with extortion or it had to do with the contract work of a rival contractor awarded to Surjit.