Comal ISD officials said the full lockdown at Canyon High School in New Braunfels was lifted at about 11:15 a.m. Friday.
A threatening phone call received earler in the morning had caused the lockdown order.
District communications director Julie Jerome said students were not believed to be in imminent danger, but as a safety precaution, the campus was locked down after 9 a.m. Friday.
New Braunfels police said the caller reported seeing a man with a gun on the high school campus.
Officers walked the hallways and checked classrooms at the school but found no threat.
Law enforcement personnel were planning to remain on campus for the rest of the school day as the campus went to a modified lockdown, which means normal operations but limited public access to the campus.