Police said the car was stopped on the M1 in South Yorkshire and that a search later turned up firearms, offensive weapons and other material inside.
According to the BBC, the arrests are not thought to be linked to the Olympics or the anti-terror arrests made in London yesterday.
West Midlands Police confirmed that six men from the West Midlands and one from West Yorkshire were detained over three days after the car was stopped on Saturday.
The men have been arrested on suspicion of the commission, preparation, or instigation of acts of terrorism, according to reports.
The UK terrorism level currently stands at “substantial”, meaning that a terrorist attack is a “strong possibility”. There are two higher levels – “severe”, which means an attack is “highly likely”, and “critical”, when an attack is “expected imminently”.