Oslo's central train station was evacuated early Wednesday morning after a suspicious bag was found on Wednesday morning.
Norwegian police also investigated a bus following the incident, but later reported that "nothing suspicious" was found.
At the same time detectives retracted an earlier statement in which they said officers were hunting a "dangerous and unstable" man believed to identify with Anders Breivik, the gunman who killed 76 people on Friday.
Police later said the man was not connected with Breivik or with Friday's attacks.
Tension is high in the country following last week's bombing of Oslo and massacre at the island of Utoya.
Police have also been investigating whether other people may have been involved in the attacks after Breivik told a court he had "two other cells" in his organisation.
However Janne Kristiansen , the Norwegian domestic intelligence chief, told the BBC that there is no evidence linking Breivik with right-wing groups inside the country or elsewhere.
Norwegian domestic intelligence chief Janne Kristiansen told the BBC no evidence has so far been found linking Anders Behring Breivik with far-right extremists in Norway or elsewhere.
"We don't have indications that he has been part of a broader movement or that he has been in connection with other cells or that there are other cells," she told the broadcaster.
British police have been investigating possible ties between Breivik and far-right groups in the UK. The suggestion of links between the gunman and the English Defence League has also prompted a review into extremist groups in Britain.