The woman told police she ran into the three men at the main square after she had left a student party.
They walked with her to the national theatre, where she says they raped her, newspaper Bergens Tidende reports.
“The perpetrators are Norwegian and spoke with Bergen and Østlandet dialects,” police investigator Rigmor Isehaug told the newspaper.
Police are examining surveillance footage they believe may help them identify the men.
The woman went to a rape crisis centre shortly after the alleged attack, enabling police to secure biological evidence.
Police said the woman was wearing a party costume, without providing details about its appearance.
The rape took place between 3.15am and 4am on Sunday. Police are asking for assistance from anyone who believes they may have seen the group.