The 29-year-old star - who shot to fame aged 12 as a member of the New Mickey Mouse Club - claims he is still not fully comfortable either as a singer or a performer, despite winning several awards for his work.
He said: "I think I`m equally insecure about both of them. I`ve been doing this for two thirds of my life and I still consider myself pretty young but I think that`s the part you battle with all the time.
"When you`re creating your art, that`s the best part. Your senses are on a creative high and then the part where everyone gets to see it and comment on it, that`s the part I think you battle with until you die.
"It`s absolutely terrifying."
Justin doesn`t want to be known only for either his acting or singing talents and thinks his early work on the children`s TV show gave him a solid grounding in both professions.
Justin - who voices the character Boo-Boo Bear in upcoming animated movie `Yogi Bear` - added: "It`s no secret I was trained as a very young kid on a TV show with a lot of other extremely talented actors and singers - Christina Aguilera, Ryan Gosling.
"I think we were all trained in the arts, be it song, dance or acting."