Beau Levi Kennedy, 33, pleaded guilty in the Brisbane District Court on Friday, saying he had made a "massive mistake" while high on drugs when he made the hoax call on October 29, 2018.

But Judge Michael Byrne QC says by uttering "only a handful of words", Kennedy committed a very serious offence.

The court heard Kennedy called the Brisbane Supreme and District courts from a public phone about 8.45am, telling a staff member: "There is a bomb hidden somewhere in court."

The police's explosives squad responded with dogs, searching the building looking for a bomb.

The courts were shut for two-and-a-half hours.

No bomb was found.

Among the people evacuated were those held in the cells in the building.

Judge Byrne says the evacuation of prisoners raised the possibility of a public safety issue, over and above the bomb threat.

"The opportunity for escape or disruption by one of those persons is patent," he told Kennedy.

Judge Byrne said the hoax call was "an affront to the administration of justice" and "an attack on one of the central institutions of the state".

Barrister Matt Jackson told the court Kennedy was high on the drug ice when he made the call.

He had also lost his job and his relationship with the mother of his three daughters shortly before he committed the offence.

Judge Byrne sentenced Kennedy to 12 months in prison, but ordered his release from jail in a month.

Australian Associated Press