The incident was reported yesterday.
The boy, Sanjay, was sleeping outside his house when the big cat dragged him away.
The family members told the police the boy was missing since morning.
His body was later recovered from a forest area behind a primary school, said a police officer.
After the incident, the angry villagers blocked traffic on the Bahraich-Ramgaon road for around three hours.
Forest Range Officer Rustom Pervez said the pugmarks found in the area confirmed it to be a leopard attack, adding that the initial compensation was paid to the family members of the boy and the body sent for a post-mortem.