Passengers were forced to evacuate the plane after it landed in Montreal on Wednesday morning (July 29).
Flight BA274 set off from Las Vegas at 9.25pm local time, and was due to arrive in London.
However it was diverted and landed in Montreal, Canada, at 5.47am local time.
There were 312 passengers on board, who disembarked from the plane upon arrival at the airport.
They are said to be safe.
British Airways said in a statement: "Our flight from Las Vegas to Heathrow landed safely this morning at Montreal and customers left the aircraft as normal after the captain took the decision to divert the aircraft as a precaution.
"The safety and security of our customers, crew and aircraft are our highest priorities at all times.
"We are looking after the customers and will provide hotel rooms for them and will rebook them to other flights as soon as we can.
"We are working with the Canadian authorities and giving them our fullest support."
Canadian authorities are now investigating the bomb threat.