No gunshots were fired and the student suspected of bringing the gun has been arrested, but police believe the student gave the gun to another student, according to KRIV FOX 26.
Live video from the KRIV FOX 26 helicopter shows the SWAT team as well as at least one K-9 unit responding to the situation.
Reuters reports that police learned of the weapon around 11:00 a.m.
North Forest High School is located in northeastern Houston and is one of 11 schools in the North Forest Independent School District. The school was rated as "academically unacceptable" by the Texas Education Agency in 2009.
KRIV FOX 26 reports that the North Forest High School is no longer on lockdown after authorities found that the student did not actually bring a gun to campus.
"It was all a big to-do for nothing," Sue Davis, a spokeswoman for the school district told Reuters. "When you have a report like that, you have to take it seriously."