The victim has been identified as Santosh Kumar, 24, cousin of JD-U's Gaya district (rural) president Abhay Kushwaha, police said, adding that they were investigating whether it was Naxal incident.
Kushwaha's brother-in-law Jai Hind was seriously injured in the incident.
Gaya Senior Superintendent of Police Manu Maharaj said, "The bomb was in a parcel sent to Kushwaha's house in Kujati village under Chandauti police station.
"It had wires attached to it and the two persons were putting it aside when it exploded. Kumar died on the spot." The explosion was not a strong one, as the impact was limited to a small area only, he said.
"We are investigating the matter. We cannot say right now whether it is a Naxal incident or somebody did it due to personal enmity," the SSP said. Meanwhile, the injured person has been admitted to Anugrah Narayan Magadh Medical College and Hospital.