The 18-year-old singer pulled up next to a group of supporters waiting outside the Tonight Show with Jay Leno studio on Wednesday (June 27), where Bieber was due to film an appearance.
Accompanied by a guitarist, Bieber then treated fans to a stripped-back rendition of his global hit before driving off again, leaving them screaming behind.
The surprise came little over a week after the 'Baby' singer was filmed blasting his fans for being "impatient" and "not very respectful" while he waited at an airport for girlfriend Selena Gomez.
Bieber confirmed this week that 'As Long As You Love Me' will be the second single released from his third studio album Believe.
The LP beat Cheryl Cole's A Million Lights to the top of the UK album chart and has reached number one in nine other countries.