The miscreants came in a car and hurled the grenade towards a group of people around 6.30 pm near a wine shop at the railway crossing in Basugaon town, they said, adding one person died on the spot while four others were hurt.
The attack took place in midst of the culmination of the Durga Puja festival and hundreds of people were returning from the immersion procession at that time.
Additional police and paramilitary forces have been rushed to the spot from the district headquarters of Kajalgaon.
Unofficial sources said police recovered another live grenade from the spot. However, officials remain tight-lipped about the recovery.