The Prime Minister said Dr Mahathir deserved the Best Actor Academy Award for his "unprincipled ways".
"He's the No 1 actor. Previously, he cursed Anwar as the most terrible person," Najib said, referring to PKR leader Datuk Seri Anwar Ibrahim.
"He used words I do not even dare to repeat. And yet he can casually meet Anwar in the courtroom and shake his hand.
"I cannot do the things he (Dr Mahathir) does. A person must have principles in politics," Najib said at the launch of the Jerantut Barisan Nasional machinery here Wednesday.
He argued that Dr Mahathir was also being used by the DAP-led Opposition to split Malay votes.
During the event, Najib also announced the setting up of an Urban Transformation Centre in Jerantut.