Six people, including a woman, were arrested in raids across England on Monday on suspicion of terrorism offences, police said.
Four men were arrested in Derby. They were aged 22, 27, 35 and 36 years. Another man, 27, was arrested in Burton upon Trent. A 32-year-old woman was arrested in London.
They were arrested on suspicion of preparing an act of terrorism in Britain, and are in police custody.
Also, six properties in Derby, Burton and London are being searched, according to the Mirror.
The operation was led by the North East counter terrorism unit. Local officers of Derbyshire, Staffordshire and the Metropolitan Police were also involved.
Police officers will be patrolling the areas to address concerns of residents, the police said.
Police is present in large numbers in Leopold Street in Derby, but they have not confirmed if they are a part of the anti-terror investigation.
Steven Allen, 32, who lives in Leopold Street, told BBC: "I've just come out of my flat, saw a police car there, thought it a bit odd.
"I heard absolutely nothing, I literally got out my flat door, saw a police car, saw the vans.
"It's usually a very quiet street. It's just such a shock to the system."
Another local who owns a shop nearby said, "It's sad and scary. It's not good for the community and the people who live round here. When I came to work I heard the news and it's a big shock."