Five men in their twenties and a 37-year-old woman were detained on Wednesday on suspicion of being members of the banned far-right group National Action.
They were held under anti-terrorism legislation and several properties were being searched.
A string of counter-terrorism units, including from the West Midlands, north-west, south-east and east England were involved in the operation.
“The arrests were pre-planned and intelligence-led; there was no threat to the public’s safety,” a spokesperson for West Midlands Police said.
National Action is a neo-Nazi organization described as a terrorist group by the UK government.
The group became the first far-right group to be outlawed in Britain last year after the murder of Member of Parliament Jo Cox, whose killing the group had praised.
In July, a senior police chief said the number of referrals to the authorities about suspected right-wing extremists had doubled since the murder of Cox, who was killed in June last year by a loner obsessed with Nazis and white supremacist ideology.