Sky's Trygve Sorvaag, reporting from the Oslo court complex, said the incident occurred near the security examination point.
There was a flurry of activity outside the Oslo court after the incident
Sorvaag said: "The man is now in hospital with serious injuries.
"Police said he was a Norwegian citizen."
The incident comes amid gripping testimony from several survivors of Breivik's attack on the island of Utoya, which claimed the lives of 69 people.