OKLAHOMA CITY - Authorities said another school is threat under investigation.

The fourth threat investigation involving an Oklahoma school this month was Tuesday at the Classen School of Advanced Studies (SAS) in Oklahoma City.

Oklahoma City Public Schools (OKCPS) said a student with a small knife was taken into custody Tuesday. That was after Classen SAS received a report of a concerning social media post.

A student, who wanted to remain anonymous, told News 9 that post showed a gun and warned people not to go to school.

OKCPS confirmed a search for a gun on school grounds came up empty. It said this was an isolated incident.

On March 13, Edmond police announced a 16-year-old former Edmond North student had components of explosives in his home.

Then just last week, Lawton Public Schools ruled out a threat at Lawton High School after rumors began to spread.

And just Tuesday, a threat investigation in Konawa sent students home early but the Seminole County Sheriff's Office said they believe that threat was a hoax.