The 43-year-old Larsen is accused of having raped a member of the party’s youth wing after the county branch's annual conference in Suldal, south-western Norway, on Saturday night.
Formal charges were filed in the case on Tuesday.
At a hastily convened press conference, the party announced on Tuesday evening that party leader Trine Skei Grande was aware of the allegations and had been in touch with the 17-year-old girl.
“The Rogaland branch of the Liberal Party (Venstre) has known about the matter for a while and my client says she has received plenty of support from the party,” the girl’s lawyer, Berit Johannessen, told newspaper Verdens Gang (VG).
Local party chief Per A. Thorbjørnsen said Larsen was on sick leave had had been admitted to hospital.
He said Larsen admitted having sex with the girl but denied raping her.