The incident, part of an ongoing investigation, took place just before 7pm at an address in Harlesden Road.
The woman, in her twenties, is one of the subjects of the investigation and was taken to hospital by London Ambulance Service where she remains in a serious but stable condition.
She has not been placed under arrest due to her condition but is under police guard at the hospital, the Metropolitan Police said.
Four arrests were made including a 20-year-old woman and 16-year-old male at the address, a 20-year-old man near the address and a 43-year-old woman who was arrested shortly after, in Kent.
Two further arrests were made when a man and woman, both 28, returned to the address later that night.
They have all been arrested on suspicion of the "commission, preparation and instigation of terrorist acts under section 41 of the terrorism act 2000" and are currently in custody at a south London police station.
Police clarified that the address had been under observation as part of an ongoing operation and that it was not related to a counter-terrorism arrest made earlier that day on Whitehall.
Police fired CS gas, a powerful form of tear gas, into the property which is still being searched along with two other London addresses.
Hours before the Brent raid a man was arrested on Whitehall, between parliament and Downing Street, with a backpack full of knives.
The raid and subsequent shooting has been referred Independent Police Complaints Commission and the Met's Directorate of Professional Standards in line with police policy.
Police have said searches at the property are ongoing, as well as other searches at linked addresses.
Deputy Assistant Commissioner Neil Basu, Senior National Co-ordinator for Counter Terrorism Policing said: "There are constant acts of immense bravery by officers - armed and unarmed - those that the public see when our officers run towards danger, just like yesterday, but a huge amount of unseen work that the public will never know about from us and our brilliant security services.
"I would also like to thank the public for their continued help and support. No matter how hard we try it is communities that will defeat terrorism and we rely on your vigilance.
"Please continue to let us know of any suspicions or concerns you may have. No call is ever a waste of our time and every call is treated seriously and confidentially and investigated."
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