The High School Musical star, who voices the film's protagonist - a 12-year-old boy named Ted - was walking the red carpet when he accidentally dropped the reported prophylactic while pulling his hand out of his pocket.
The incident in question was captured on video and has since been posted on YouTube.
In the video, Efron turns to his publicist to ask her to hold something, but while he hands it over, a gold-foiled packet can be seen falling out of his right pocket. He quickly picks up the item before posing for pictures.
Efron's representatives have not yet commented on the incident.
Efron was rumoured to be dating Taylor Swift, who also voices a character in The Lorax, but the two recently denied these reports by performing a duet on The Ellen DeGeneres Show.
The actor has also been romantically linked to Mirror Mirror star Lily Collins.
The Lorax opens in cinemas in the US on March 2 and July 27 in the UK.
Watch the trailer for The Lorax, introduced by Zac Efron, below: