Communist Party of India-Marxist worker Ravindran was killed and four others injured when a bomb was hurled at a vehicle near Pinarayi in Kannur district on Thursday evening. The four injured were admitted to a hospital near Kannur.
CPI-M activists was celebrating the victory of their party in the elections held for the 140-member Kerala assembly when the incident happened.
Agitated CPI-M supporters blamed the incident on a right-wing organisation.
Police said violence broke out in Thrissur and in Kumarakom near Kottayam when Bharatiya Janata Party and CPI-M workers clashed.
The office of the Revolutionary Marxist Party, founded by former CPI-M leader T.P. Chandrasekharan, was attacked near Vatakara in Kozhikode district.
A memorial to Chandrasekharan, who was brutally killed a few years back, was also defaced by CPI-M workers, RMP leaders alleged.