Armed policemen stormed into the EK004 flight after air crew alerted police on certain 'remarks' being made as the plane prepared for take off, say media reports.
The flight, with 331 passengers onboard, was grounded over three hours after this incident which took place at around 8 pm (local time) on Friday, Jan 8 night.
Sky News quotes Metropolitan Police as saying that three men, aged 58, 48 and 36, have been arrested on suspicion of making a bomb threat.
According to a report in Mail Online, one allegedly made a 'verbal threat' as the plane taxied towards the Terminal 3 runway.
As per witness accounts, the main suspect reportedly looked like a white man.
Passengers were asked to empty the overhead lockers to search for potential explosives.
Despite the security threat, Heathrow continues to remain open.
"We are aware of a security incident at Heathrow. The airport and terminal remains open. We have not found anything," a Scotland Yard source was quoted as saying by Mail Online.