Sources said the explosion took place near the Shaympur Bhitta Police Station area of the district, the first attack during the state polls.
Further reports said a special task force of Bihar police and CRPF personnel have cordoned off the area and intensified the combing operation against the Naxalites.
"Naxalism and Left Wing Extremism today pose a great threat to our national security. We recognize that there is a development deficit in all parts of our country. But we should be equally clear that the Indian State cannot and will not allow its authority to be challenged," said the PM.