Justin Bieber has confessed he was very scared before kissing girlfriend Selena Gomez for the first time but he insists the smooch was the "best" of his life.

Justin Bieber has confessed he was scared before kissing Selena Gomez for the first time.

The 18-year-old pop superstar has been dating the gorgeous 20-year-old actress for 19 months and he recalls being very nervous before their debut smooch.

Speaking about the kiss with We Love Pop magazine, he said: "It was scary and spontaneous and it was just awesome ... It was the best (kiss) of my life."

Despite being in a committed relationship for several months, Justin claims he still doesn't understand women.

The 'Boyfriend' singer spends a lot if his time trying to guess what Selena is thinking or what type of mood she is in.

He said: "I don't think I'll ever stop learning about girls. You never know whether they're going to be happy or sad, do you? You kinda have to hope that they're going to be in a good mood."