The ISI operative, identified as Sudhanshu Sudhakar was an ex-Army sepoy. He was dismissed from the Army five years ago and was court marshaled for his involvement in a recruitment scam, media reports said.
Bihar police spokesperson Neel Mani said, "Sudhanshu's lead was given by the Intelligence Bureau. We arrested him along with vital documents related to military deployment on Western borders."
"We have registered a case under the official secrets act. He is being interrogated by military officials and intelligence officers," he said.
According to Bihar police, important documents revealing military secrets was recovered from him.
Sudhanshu was trapped through a surveillance of telephone, where he was regularly in touch with ISI agents in Pak and Nepal for over two years, police said.