The youth identified as Rajeesh from Allanchery and said to be the member of Democratic Youth Federation of India was taken into custody last night, based on a complaint by local RSS leaders, and arrested today, police said.
He had posted "offencive" statements against Modi on his facebook page, they said.
This is the third instance of arrest of youths in Kerala for derogatory remarks against Modi after he became Prime Minister.
In earlier two incidents, nine students of Sree Krishna College in Guruvayur and the Principal and some students of a polytechnic college in Kuzhur near Thrissur were arrested in June last for carrying unsavoury remarks against Modi in their campus magazines.
In both the institutions, the student unions are controlled by CPI-M's student outfit Student's Federation of India (SFI).