"He's been charged," a Scotland Yard spokeswoman said on Friday, referring to 45-year-old Alwasila Alhibr Wassila who was arrested at Heathrow.
The Sudanese national was coming off a Virgin Atlantic flight from Dulles airport in Washington on Wednesday.
Wassila faces three charges: one for carrying ammunition, another for carrying "prohibited ammunition" and a third regarding the "possession of dangerous articles on an aeroplane", the spokeswoman said.
Wassila is due to appear at a central London police station later on Friday.
The spokeswoman could not confirm a BBC report, quoting airport sources, that five bullets of two types had been found in a pocket of Wassila's coat.
The incident has raised questions about security at Dulles airport, less than a week after the US national terrorist threat level was lowered from elevated to high.
Wassila was initially arrested under the Firearms Act when he stopped at a security checkpoint soon after disembarking from Virgin Atlantic Flight VS 022 on Wednesday.
In transit for a flight to Dubai, Wassila was taken to the Heathrow airport police station for questioning after he was picked up in Terminal Three's transit lounge.
A few hours later, the police said he was being arrested under Section 41 of Britain's Terrorism Act 2000, which refers to "alleged involvement in the commission, preparation or instigation of acts of terrorism".
Virgin Atlantic said "the item seized did not pose a threat to our aircraft", while BBC television reported that the man was not on any known "terror watchlist".
Heathrow, one of the world's busiest airports, was on a heightened state of alert throughout the Christmas and New Year's holidays, as US officials feared a repeat of the 11 September attacks.