Police arrested the 14-year-old on suspicion of felony harassment after reading a post she allegedly made on a Facebook page called PTHS Confessions.
In the comment, which was posted Sunday night, the girl said she would bring a shotgun to school to confront a student who was bullying her, according to Port Townsend Police.
The girl was arrested in school on Tuesday and is being held at a juvenile detention center until her Wednesday court appearance.
During a police interview, the girl admitted to leaving the comment, but claimed it was a joke, according to police.
Police say there's no indication the girl actually planned on carrying out the threat, but school officials insisted that all threats -- even those made in jest -- will be taken seriously.
"High school is a tough enough stage in life as it is," school resource officer Garin Williams said in a news release. "It doesn't need to be compounded with the fear that someone is bringing a gun to class."