Those arrested have been identified as Deepu, Lambu Pradeep, Rejith and CPI(M)'s local committee member at Orkattery Padayankandi Ravindran. The name of the fifth person was not disclosed by police.
While Ravindran was arrested for helping the culprits in identifying Chandrasekharan before killing, the remaining were accused of helping the culprits for hiding the weapon used for the murder, police said.
Earlier a look out notice was issued against 12 people as part of the investigation into the murder.
Chandrasekharan, 50, was murdered at Vallikkad near Vatakara in Kozhikode district on May 4.
The assailants who came by a car had attacked him while he was riding a motorcycle alone. Country-made bombs were hurled at him and when he fell off the motorcycle, he was hacked to death with sharp-edged weapons.
Police said the assailants had attempted to mislead them in their probe by using a fake number car plate.
A former CPI(M) leader in the party stronghold Onjiyam in Kozhikode district, Chandrasekharan was expelled a few years ago after falling out with the leadership. He later joined RMP floated by CPI(M) activists who had either quit the party over ideological issues or expelled for anti-party activities.