Witnesses told The Star-Tribune in Casper that someone shot a professor and then stabbed him repeatedly at Casper College.
Two died on campus, and another died in an off-campus neighborhood.
NBC affiliate KCWY reported two victims were "student age" while the other was a faculty member.
The suspect in the incident appears to have committed suicide, although KCWY said no guns were involved.
Police responded to Casper College about 9 a.m. with reports of one injured, The Associated Press said.
Casper College issued an emergency alert on its webpage, telling students to stay away from campus and cancelling all classes and activities.
The incident happened in the Wold Physical Science Center, the Star-Tribune said.
School spokesman Rich Fujita told the newspaper early on that police “are about as certain as they can be at this point – they tell me that the suspect is deceased.”
Student Delina Barbosa told the local paper that a school secretary interrupted her chemistry class, banging on the door and telling students, “You guys need to evacuate right now. This is not a drill.”
Other witnesses told the newspaper that, after an evacuation, students spoke about a bow-and-arrow attack on a professor.
On its Facebook page, Casper College said grief counselors are available.
"Casper College President, Dr. Walter Nolte just indicated that all employees who do not have duties today related to the tragedy may close their offices and leave campus," the statement read. "Please note that counselors are available on the second floor of the Gateway Building on a walk-in basis."