Authorities say the man was wounded Monday afternoon outside an entrance to Kirkland House, one of a dozen dorms on the university's campus in the Boston suburb of Cambridge. He's hospitalized in stable condition.
Police say it's unclear if he's a student.
A witness tells The Harvard Crimson student newspaper the victim appeared to be "college-aged" and was bleeding but conscious.
Kirkland House administrators have sent an e-mail to students informing them of the shooting and asking them to cooperate with police and staff.
The university says the shooting appears to be an "isolated" incident. It says Kirkland House residents are being asked to remain at the undergraduate dormitory but other members of the university community can resume normal activities.
Police are now searching for suspects. A Cambridge police sergeant tells CBS Station WBZ in Boston they are looking for three college aged men.
The alleged shooters and the victim are not believed to be Harvard University students.
The Kirkland House is an undergraduate housing building near Mount Auburn Street. Officers are going door-to-door in the 300-student dormitory, asking students if they witnessed anything, WBZ reports.
In a letter sent to students in the dorm shortly after the shooting, the university asked students to stay in the dining hall, basement or the JCR (hallway) until it was safe to return to their rooms.
Shortly after 7 p.m., students were allowed back into their dorms, but asked to remain in the building as police continued to investigate the shooting. Officials believe the suspects have left the area. "All indications thus far are that the incident was isolated and that the suspects have fled the area," the school said in a statement.
Kathleen Breeden, a senior at Harvard, was in the Kirkland House when the shooting happened. "I just heard three gun shots in quick succession. … We didn't really know what was going on. That was the tough part, then getting all these rumors," she told WBZ
Immediately after the shooting, Boston transit officials were alerted of the situation and asked to search all trains and buses in the area. Nothing was found.
Harvard, Cambridge, and state police are on the scene and are interviewing potential witnesses.