The 18-year-old singer, who is currently dating Selena Gomez, laughed and asked for the "next question" when The Sunday Times Magazine quizzed him about his sex life.
However, Bieber was more at ease discussing his fans' interest in his anatomy, revealing that followers worldwide have now nicknamed his genitalia.
"The fans named my penis 'Jerry'," he revealed. "Which is funny."
The teen idol also revealed that it now takes work to appear fresh-faced, saying: "I shave. But not often. I only grow a little moustache. It's good to not have that much, right."
Bieber was last year hit with a paternity suit by a fan named Mariah Yeater, who claimed she fell pregnant after sleeping with the 'Boyfriend' singer at a concert.
The star went on to write a song about the false accusations, which he has described as his own version of Michael Jackson's 'Billie Jean'.
Watch Justin Bieber's video for 'Boyfriend' below: