Additional Superintendent of Police (East) Surendra Dwivedi said Mustaquim (45), Shayad (27) and Zeeshan (18) were injured by bomb shrapnel and have been hospitalised.
The attack took place in Babhanmai village, police said.
He added that no complaint has been lodged so far in this connection. A case will be registered once a complaint is filed, the police official said.
Police are probing the matter.