FBI (search) agents arrested a San Antonio man Tuesday accused of planting a note on a Southwest Airlines flight claiming there was a bomb on board.

The threat forced a temporary shut down at Houston's Hobby Airport, and the plane had to be evacuated and then searched after a passenger found the note in a seat pocket during a flight from Dallas to Houston on Friday.

No explosives were found.

Elias Jeremiah Cervantez (search), 20, of San Antonio, was charged Monday with making a false bomb threat to an aircraft. He confessed to FBI agents that he wrote the note on a gum wrapper, according to an affidavit signed by special agent Jamaal C. King.

The note read, "There's a bomb on the plane!" Another note asked whoever found it to call a phone number and tell them. It was accompanied by a drawing of a happy face.

If convicted, Cervantez faces up to five years in prison and a fine of up to $250,000. It wasn't immediately clear if he had an attorney who could comment.

U.S. Attorney Chuck Rosenberg (search) said investigators had determined the note was left on the plane during an earlier flight from Odessa to Dallas.

"People need to understand that we take these threats very seriously, and that we will prosecute anyone who threatens an airline even, as here, when the threat turns out to be a hoax," U.S. Attorney Chuck Rosenberg's statement said. "Not funny, don't do it."