The six were taken to a south-east London police station, the force spokesman said.
A 29-year-old man was arrested in the street in west London, a 21-year-old man and the women were arrested at a separate residential premises in west London, and three other men, aged 18, 24, and 26, were arrested in east London.
Searches under the Terrorism Act 2000 are being carried out at eight residential premises in east, west and north London and one business premises in east London.
Public safety remains our overriding concern.
More top news
With harmful pollutants at record levels the Mayor of London's campaign aims to highlight the impact air quality can have on health.
A firework was shot into a London bus sending frightened passengers running with fear.
Abdul Samad, 28, was stabbed outside his family home in Little Venice last night and died an hour later in hospital.