Sky News reported two young women, thought to be airport workers, had been arrested.
"We can confirm that officers from the Met's Aviation Policing Command are investigating an allegation of fraud," said a spokesperson for the Metropolitan Police.
"Detectives arrested two women from Surrey, aged 24 and 20, on suspicion of fraud and money laundering on Wednesday, 3 August. They have been arrested in relation to an allegation that money has been fraudulently taken from a bank account. Other matters have come to light during the enquiries and form part of the ongoing investigation.
"The women were taken into custody at a west London police station and have subsquently been bailed to return to the police station in late November. Detectives searched a residential address in Surrey under the Police And Criminal Evidence Act.
"Enquiries are ongoing."
Earlier this year a 38-year-old man was held by police after he broke through a security cordon at the airport, climbed aboard an empty 747 and locked himself in the cockpit.
Today a spokesperson at Heathrow said she couldn't comment on the specifics of an ongoing police investigation.
“Our top priority is the security and safety of our passengers and colleagues and we have taken appropriate action until the investigation is completed," she added.