A 40-year-old and a 55-year-old were arrested at addresses in Barnet, a 52-year-old in Watford and a 22-year-old in Harrow.
Six other men aged 29, 39, 42, 49 and two aged 20, were arrested at the same location in Harrow on suspicion of assisting an offender.
All 10 men have been taken into custody.
Commander Helen Flanagan, head of Counter Terrorism Policing London, said the arrests, which took place around 01:00 GMT, are part of “a long-running investigation and part of our ongoing work to disrupt malign activity where we suspect it”.
“We understand the public may be concerned, in particular the Jewish community, and as always, I would ask them to remain vigilant and if they see or hear anything that concerns them, then to contact us,” she added.
The arrests and search activity is being led by Counter Terrorism Policing London.