The additional district sessions court at Thalassery also imposed a fine of Rs 70,000 each.
Judge G P N Vinod directed them to pay the fine amount to the legal heirs of the deceased Ashraf.
The prosecution case was that the six had barged into an automobile shop when Ashraf had gone there to buy a vehicle and hacked him to death.
The incident happened on February 5, 2002.
The trial began in October 2011. The prosecution produced 25 documents to prove the charges, public prosecutor B P Sasidharan said.