Armwood High School in Seffner was placed on lockdown Wednesday morning, after a student was found with a knife and bullets.
According to Hillsborough County Schools, a student threatened another student which prompted a search.
Officials found the knife and bullets, but no gun.
Police have arrested a student, and search the school campus as a precaution.
The lockdown at Armwood High was lifted shortly after 2:30 p.m.