According to Sky News, the witnesses claim the gunmen was accompanied by a suicide bomber who died after blowing himself up.
Nobody else was killed.
It has been reported the extremists attacked the College of Administrative and Business Studies in Potiskum, Yobe State, at around 7:00am British time, on Friday.
The gunman was caught by locals and beaten.
It has not yet been confirmed whether the duo were from the extremist group, Boko Haram.
It also remains unclear whether the gunman has been detained by police.
Musa Ahmed, a student at the College, told Reuters: "We came out from lectures when we saw two people at the gate...he brought out a gun and started shooting."
The Nigerian army recently rescued hundreds of females from Boko Haram in the Sambisa Forest in the north of the country. It declined to say how many militants were killed in the operation.
The girls were not the Chibok schoolgirls, who were kidnapped by the extremist group in April last year.
The country's recently elected Muslim president, Muhammadu Buhari, has told Premier finding the Chibok schoolgirls is a "priority".
In the last few months, the Nigerian army alongside forces from neighbouring African countries have regained hundreds of square miles of territory from Boko Haram.
