The hunky actor knows he is good looking but regularly checks with his therapist to ensure he isn't overly preoccupied with his appearance.
He said: "I've had years of psychiatry, and I ask about every six months -- it's sort of like getting your oil checked -- I ask, 'I'm not an actual narcissist, am I?'
"The learned men of psychiatry assure me that I meet none of the medical criteria. The fact that we can even ponder the question immediately disqualifies me from being one."
The 'Sex Tape' actor also claimed his appearance has prevented him from being offered "deep or interesting" roles and thinks it is only now he is getting older that he is able to properly show off his range.
He told the New York Times magazine: "There's this unbelievable bias and prejudice against quote-unquote good-looking people, that they can't be in pain or they can't have rough lives or be deep or interesting.
"They can't be any of the things that you long to play as an actor. I'm getting to play those parts now and loving it. When I was a teen idol, I was so goddamn pretty I wouldn't have taken myself seriously."
And Rob, 50, admitted he was a "nerd" who no one thought of as "cool" until he found fame.
He added: "My deep dark secret is that I was a nerd in school. I liked the theater. I liked to study. I wasn't very good at sports. It took being famous to make me cool, which, by the way, I never forgot."