The activists were protesting against the arrest of 29 people, including Ex-MLA Rajaram Singh May two last.
During the protest the CPI(ML) activists clashed with the policemen and pelted stones at them injuring seven of the cops, sources said.
The injured policemen, including three women, were admitted to hospital, they said.
The police later lathicharged on the protesting CPI(M-L) workers to disperse them, sources said.
The police had arrested 29 people on May two last following an incident of violence and arson by a mob, comprising local people and opposition workers to protest the murder of Sonhathu panchyat mukhiya Devendra Singh alias Chhotu by the armed assailants on March 29 last.
The CPI (M-L) and other opposition parties have demanded a CBI probe in the mukhiya's murder and the police lathicharge on the protesters.