The arrests were part of a pre-planned intelligence-led operation by the British Metropolitan Police.
Five men and a woman were arrested on suspicion of the commission, preparation or instigation of acts of terrorism.
A 24-year-old man was tasered during his arrest, but did not require hospital treatment.
A 29-year-old man was arrested in the street in west London, a 21-year-old man and a 30-year-old woman were held at separate residential premises in west London, and two other men, aged 18 and 26, were arrested with the 24-year-old in east London.
>Police have said that the arrests are not linked to the Olympics.
The six are being held at a south-east London police station.
Elsewhere, almost 50 people were evacuated from a coach after armed police closed Britain's M6 near Lichfield.
The coach was going from Preston to London.
Reports had suggested that a man was seen pouring liquid into a smoking bag on board the coach.
British police have said that no-one has been injured, there is no danger to passengers and no-one is being treated as a suspect.