The incident took place when the army personnel were cleaning some weapons and explosives at 21 Rashtriya Rifles camp in Handwara, 80 kms from here, a police spokesman said.
Six army personnel were injured and immediately rushed to the hospital, he added.
The army unit had yesterday seized a large quantity of arms and ammunition from a militant hideout in the Mouldari forests but it was not clear yet if the exploded grenade was from the seized lot.