Six men from the West Midlands and one man from West Yorkshire are being questioned over plans to carry out acts of terrorism.
Six of them are in their twenties and from the Sparkhill, Moseley, Alum Rock and Smethwick areas of the West Midlands.
The arrests followed a routine vehicle stop by police on the M1 motorway at the weekend.
The car was impounded on suspicion of having no insurance.
Firearms, offensive weapons and other material were later found hidden inside.