Armed police led two men away in handcuffs after an object was thrown over the gate of the residence at Kensington Palace Gardens at around 1.40pm.
The Metropolitan Police said that one man was arrested at the scene on suspicion of arson, while the other man was arrested for allegedly assaulting a security guard. The security guard sustained minor injuries and was given first aid at the scene.
The two men remain in police custody at a central London police station.
Firefighters from the London Fire Brigade attended the scene after the object set a number of bushes alight.
They were quickly able to get the blaze under control.
The London Fire Brigade told The Evening Standard: “We were called to bushes alight at 1.41pm. It was under control by 1.50pm.
“One fire engine attended and there were no reported injuries.”
The residence is just metres away from the official home of the Duke and Duchess of Cambridge - Kensington Palace.