It was around 10pm last Sunday that a bag with dangerous contents was found in Kungsträdgården.
The site was cordoned off, which affected both people on site and traffic.
The national bomb defense neutralized the object and an investigation into attempted mass destruction was launched.
During Friday, several people could therefore be arrested.
- Since last Sunday, we have worked intensively with a large resource and all the specialist skills that are available.
The work has led to today's arrests and the work continues, says Erik Åkerlund, local police area manager at Norrmalm Police, in a press release.
The item is currently being analyzed at the National Forensic Centre.
There are no suspicions that it was a terrorist crime, according to the police.