Passengers took to social media to report issues at check-in, with some claiming waits of several hours.
A BA spokesperson said: "We experienced a technical issue for a short time this afternoon which affected our operation at Heathrow Terminal 5.
"This has now been resolved and we’re resuming flight operations. We’ve apologised to those customers who have been inconvenienced."
A Heathrow spokesperson added: "A technical issue which affected British Airways this afternoon has now been resolved. We are working with our airport partners to assist passengers whose journeys have been disrupted and have deployed additional resource in our terminals.
"Passengers are still advised to check their flight status with British Airways before travelling to the airport due to a number of resulting cancellations. We apologise for any inconvenience caused.”
It comes after the airline was last month forced to cancel all short-haul flights at Heathrow on Saturday 25 February owing to a technical issue, with disruption spilling over into Sunday 26 February.
