The incident took place at Chakka near the airport while the Prime Minister was on the way to the airport after his engagements in the city.
Singh launched the total E-literacy Programme of Kerala Government and also laid the foundation stone of the Tata Consultancy Service (TCS) Global Learning Centre.
Police refuted the suggestion that the incident involved security lapse and claimed that the protesters were instantly halted before they could jump on to the road and obstruct movement of the motorcade.
An FIR has been lodged in connection with the incident and they would be produced in the court, police said.