Mr Khetan claimed he received a letter on May 9 stating that he had "crossed all levels" in committing sins against Hindu saints.
"It is because of you (Khetan) that Sadhvi Pragya Singh (an accused in the 2006 Malegaon blasts case) and Virendra Singh Tawde (an accused in the case of murder of rationalist Narendra Dabholkar in 2013) are in jail. People like you deserve only death punishment in a Hindu Rashtra," the letter said.
The journalist-turned-politician has written to the Union home minister seeking action in the matter. He also said that several journalists, writers and activists had been threatened by the right wing forces.
AAP chief and Delhi Chief Minister Arvind Kejriwal said the incident was "extremely shocking" and demanded action from the home minister.
Mr Khetan is the vice-chairman of the Delhi Dialogue Commission, which looks after the implementation of various polls promises made by the AAP before the 2015 Assembly polls.
He had also unsuccessfully contested the 2014 Lok Sabha election from the New Delhi constituency.
(with inputs from PTI)