It comes after four were arrested in Birmingham and one at London's Gatwick Airport last week.
West Midlands Police said today that four people were still being questioned after securing warrants of further detention, while a 59-year-old man had been bailed "with strict conditions".
"The arrests were pre-planned and intelligence-led. There was no risk to the public at any time and there is no information to suggest an attack in the UK was being planned," Marcus Beale, assistant chief constable who leads on counter terrorism for the West Midlands, said.
Belgian Mohamed Abrini has been named by British media as suspected of involvement in the Islamic State attacks in Brussels. He travelled to Birmingham last year and took photos of a soccer stadium.
Abrini is also wanted in connection with the Paris attacks.