Five men and a woman have been arrested on suspicion of being members of banned far-right terror group National Action.
The suspects, aged between 21 and 37, were arrested under the Terrorism Act on Wednesday, West Midlands Police said.
The male suspects include 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.
The female suspect is a 37-year-old, also from Banbury, the force added.
All six are being held at a police station in the West Midlands.
The arrests were part of a pre-planned operation.
Counter-terrorism officers are now carrying out searches at several properties in connection with the arrests.
National Action – the first right-wing group to be outlawed in the UK - was made a proscribed terrorist organisation in December 2016.
They are the latest in a wave of arrests of alleged National Action members since the group was banned by the Government.
Counter-terror police have detained dozens of people, including some on suspicion of plotting terror attacks, since the order formally came into effect.