Police spokesman Lars Bystrom says a small amount of drugs and a stun gun were found when officers raided the empty bus parked under the Globen concert venue in Stockholm, where Bieber was performing Wednesday.
Bystrom said Thursday they have no suspects and no one has been arrested. He declined to identify the drug, saying it had been sent to a laboratory for an analysis.
He says police acted after smelling marijuana coming from inside the bus when it was parked outside the hotel where Bieber was staying. The drug squad was alerted and searched the bus during the concert.
The Canadian singer is in Stockholm as part of a world tour.