The incident occurred when the girl had gone to a field last night, Superintendent of Police Santosh Kumar said.
The victim was admitted to the sadar hospital at Sheikhpura.
While one person was arrested, search was on for the other, he said.
In an another incident, a girl of same age was gangraped by eight persons at Sisauna in Araria district on Saturday last.
Medical examination of the girl had been completed, Superintendent of Police Akhtar Hussain said.
Police was waiting for the report, he said.