Besides, nine other personnel of the border guarding force were also injured.
Supaul Superintendent of Police D. Amarkesh said the casualties happened after the SSB personnel had come in contact with a high tension wire.
They were posted in the 45th battalion of SSB in Birpur.
According to an official of the 45th battalion of SSB, a team of 12 personnel were patrolling in the area when the mishap took place.
The injured personnel later contacted the battalion office in Birpur followed which their colleagues arrived at the spot for help and assistance.
"We have found three individuals dead on the spot while other nine personnel were critically injured. We have rescued them and admitted them to a hospital where four of them are in critical condition," an official said.