The teen superstar was on CBS's Late Show with David Letterman this week.
Justin was enthusiastically talking about all the places he has travelled to while touring, when David decided to put him to the test.
"I love it. I have a blast. I get to travel the world,' Justin told the chat show host, 'I think I've been to every continent."
At which point David asked: "How many continents are there?"
Rather than answering with a number the 17-year-old confidently began to name what he thought.
However, he was soon struggling and relied on clues from the host to get the complete list.
"Asia, North America, South America, Africa, Antarctica and the North Pole,' he said. 'Err, Canada."
"There are two more, come on. These are easy ones. You've been to both places," David hinted.
Justin then came up with Australia, which David accepted as Australasia.
During his My World Tour this year, the singer visited many countries in Europe including Germany, Italy, the UK, Spain and Belgium.
But it took another hint from the host until Justin finally twigged which continent he was missing.
"I'll give you a couple of countries in the last continent ' France..." said David.
"Europe!" Justin yelled triumphantly.