The incident occurred around 1.00 AM, police said.
The number of attackers is not yet known and CCTV footage of the area was being examined to ascertain the same, they said.
An FIR under relevant provisions of the Explosives Act has been registered and the investigation was going on to trace the culprits.
It also said that RSS has accused CPI(M) workers of carrying out the attack.
According to CCTV visuals of the attack several explosions could be seen within the boundary wall of the RSS office with many of its windows damaged in the incident.
The attack comes days after a bomb was hurled at the wall of CPI(M)’s state headquarters, AKG Centre, on the night of June 30 and the attacker in that case is yet to be identified by police.