The school was notified about the threat made on Twitter through the mother of a student who had told her about it.
Police say they then received a call from the school at about 8:50 a.m. Tuesday.
That's when the school, located on 11000 Scott on the city's south side, went into lockdown.
Officers arrived and searched the campus.
After working with school administrators and finding no danger at the school, officials say they agreed to lift the lockdown.
Police say they do have possible suspects but are still investigating that aspect of the case.
They warned again that they take these types of threats seriously and students who make threats can be arrested.
"It is something that can get you into a lot of trouble. It is not something that the district attorney's office or the Houston Police Department finds the least bit funny. We will seek charges and prosecution on anybody that makes these threats jokingly or seriously," said Captain W. McPherson with the Houston Police Department.
HPD investigating report of threat @KIPPHouston Sunnyside High School 11000 Scott. School on lockdown however no immediate threat found. Investigation currently ongoing. PIO on scene. pic.twitter.com/TyK1NJ5npK— Houston Police (@houstonpolice) February 27, 2018
McPherson also said the amount of threats has increased since the high school shooting in Florida two weeks ago.
Just last week, a threat was made against another KIPP school.
In that incident, police say a 12-year-old boy threatened to shoot up KIPP Sharpstown College Prep School.
SEE ALSO: NO JOKE: Schools on edge after week of lockdowns and alleged threats on social media