The body has been identified as that of 45-year-old Surendra Rajvanshi, chief of the party's scheduled caste cell in Nawada district, Station House Officer (SHO) of Sirdala police station Raj Kumar said.
"The villagers spotted the body and fished it out from the canal," the SHO said. Mr Rajvanshi was a resident of naxal-infested Ahmadi village, he said.
His family members suspected that Mr Rajvanshi's body was thrown in the canal after he was killed, the police said.
The police is investigating the matter.