A third boy was rescued by his brother.
The mishap occurred when four boys - Nitish, Nitin, Surya and Dipu - went to take bath in the river at Dahrak village in the Ramgarh police station area, Deputy Superintendent of Police Manoj Ram said.
The deceased has been identified as Nitish Kumar (14) while his elder brother Nitin Kumar (16) is missing, the deputy SP said.