Pehlu Khan and his sons were thrashed by a mob on the suspicion of cow smuggling in Alwar's Behror on Aprli 1, 2017.
Khan had died at a hospital in Alwar on April 3.
"The appeal was filed in the Rajasthan high court on Monday," Additional Advocate General R P Singh said.
An Alwar court had acquitted all six accused-- Vipin Yadav, Ravindra Kumar, Kaluram, Dayanand, Yogesh Kumar and Bheem Rathi — on August 14 this year, giving them the benefit of the doubt.
After the lower court verdict, the state government had constituted a special investigation team (SIT) to identify errors and irregularities in the investigation and fix the responsibility for botching up the investigation on individual officers.
The SIT submitted its report to the DGP last month.
Khan and others were on their way to Nuh district in Haryana from Jaipur when the cow vigilantes stopped them in Behror on the Jaipur-Delhi national highway.