The 25-year-old woman was gangraped Thursday night in Tarma village in Muzaffarpur district, about 70 km from here, police said.
"We have arrested four accused and search is on to nab the other two," police official Kanchan Kashyap said.
On Thursday, the woman along with her husband and five-year-old son were sleeping in their rented house, when the six men attacked them.
They tied her husband and son to a nearby tree and forcibly dragged her to a field and raped her, a district police official said.
The victim and her husband, who works as a labourer in a local thermal power plant, approached police Friday. The woman has identified three of the accused, police said.