Rajagopal's office is on the ground floor of a two storeyed building.
BJP state President Kummanam Rajasekharan alleged that CPI(M)'s Kannur lobby was responsible for the attack and demanded that the culprits be brought to book immediately.
Police said three motorbike borne miscreants had hurled stones at the first floor portion of the building, where one Anil Kumar resides. His car was also damaged.
A case has been registered on the basis of a complaint from Anil Kumar, police said.