The Munshi of the police station, Ramesh Kumar Singh, and Computer Operator Pradeep Kumar Yadav, who were injured in the incident, told reporters they had been using a round-shaped object wrapped in black tape as paper weight for last 3-4 months.
The blast occurred when the object fell on the ground and exploded, they said.
The impact of the explosion was so strong that the right hand of the computer operator was badly injured while the Munshi suffered burn injuries in chest, face and head.
Police officers said a crude bomb, which was recovered few months ago, was defused by keeping it in bucket full of water and someone wrapped it in a paper and applied the black tape.
Since then, the object was being used as a paper weight but it exploded today.
Deputy Superintendent of Police (HQ), Navneet Hembram said an FIR would be lodged following the investigation and stringent action would be taken against the culprits.