Five men and one woman have been arrested on suspicion of being members of the banned far-right National Action party.
Police in the West Midlands have made six counter-terror arrests and are searching several properties in connection.
The men are a 26-year-old from Cambridge, a 21-year-old from Banbury, Oxfordshire, a 28-year-old from Wolverhampton, a 26-year-old from Leicester and a 24-year-old from Stockport.
A 37-year-old woman also from Banbury, has been arrested.
The five men are being held in West Midlands, while the woman is being held in a station outside the force area.
They are held on suspicion of being concerned in the commission, preparation and instigation of acts of terrorism under Section 41 of the Terrorism Act 2000.
Officers said the arrests were connected to being members of a proscribed organisation – National Action – contrary to section 11 of the Terrorism Act.
The arrests were all pre-planned and intelligence led and there was no threat to the public’s safety.
Several counter-terrorist units from forces across the country were involved.
National Action was made a banned group in December 2016, by Home Secretary Amber Rudd, the first extreme right-wing group to be outlawed in the UK.
The proscription meant that being a member of or inviting support for the organisation is a criminal offence, carrying a sentence of up to 10 years’ imprisonment.
In the official list of proscribed groups, it is described as a “racist neo-Nazi group” that was established in 2013 and has branches across the UK which “conduct provocative street demonstrations and stunts aimed at intimidating local communities”.
When she banned the group, Ms Rudd said: “National Action is a racist, anti-Semitic and homophobic organisation which stirs up hatred, glorifies violence and promotes a vile ideology, and I will not stand for it.
“It has absolutely no place in a Britain that works for everyone.”
Police last arrested 11 people across England and Wales in September 2017 on suspicion of being members of the banned group.