The incident took place at around 12.30 pm yesterday, they said.
The area near Koothparambu is a BJP stronghold.
The activist, Ashokan, a block panchayat president, had quit BJP before the local body polls in November last year.
Police said as there were threats to him, he had been provided security.
His gunman, Renjith, was injured in the attack.
Window panes of the house were also damaged.
Some persons having affiliation to BJP have been named in the FIR, police said.