No passengers were aboard the aircraft, which was parked far away from the terminals at the time of the incident, according to a tweet posted by airport staff.
The incident marks yet another setback for Boeing's next-generation airliner. The Federal Aviation Administration grounded the entire fleet of Dreamliners worldwide in January following several on-board fires.
The fires were found to be caused by an issue with the aircraft's lithium-ion batteries. Dreamliner flights resumed in May after Boeing and its suppliers were able to install a FAA-approved fix for the battery systems.
It's unknown whether the batteries are again to blame in Friday's incident involving the Ethiopian Airlines aircraft. Television footage showed the Dreamliner surrounded by foam after a fire crew responded to the emergency.
Heathrow Airport tweeted that it has since resumed flights.
