A Queensland Police Service senior constable has been fined $1,500 over an incident captured on video in which he pulled a gun on a couple for allegedly speeding along an outback highway.

Key points: Senior Constable Stephen Flanagan was found guilty last year

Senior Constable Stephen Flanagan was found guilty last year No conviction was recorded as Flanagan suffered from undiagnosed PTSD

No conviction was recorded as Flanagan suffered from undiagnosed PTSD Flanagan has since been fined $1,500 for the incident

Senior Constable Stephen Flanagan was found guilty of assault and deprivation of liberty in a Brisbane court in December last year over an incident on the Landsborough Highway near Longreach in May 2015.

The recording showed the police officer swearing and honking on the highway before pulling his gun on the couple.

Flanagan assaulted the man when he held the gun to his back.

Magistrate Paul Kluck ordered no conviction to be recorded and accepted the officer suffered from undiagnosed post-traumatic stress disorder (PTSD).

In sentencing submissions, defence lawyer Stephen Zillman presented a psychological report that showed his client had been diagnosed with PTSD, of which he was unaware at the time of the offence.

Lee Povey (right) and his partner Anna Lisa Cruse were assaulted by Flanagan when driving home to Mount Isa last year. ( AAP: Dan Peled )

"A mature man of mid-40s, a police officer of some 26 years, commits these two offences — one would immediately question how that could be so," Mr Zillman said.

He said the answer was in the psychological report, because otherwise the behaviour was "quite bizarre".

Prosecutor Jodie Wooldridge said while police officers did confront some challenging situations, they had a responsibility to uphold the law.

"It remains highly relevant that the defendant committed the offences whilst on duty as a police officer, and in committing the offences has acted contrary to his sworn duty as a police officer to uphold the law," she said.

"To have acted as he did, and to have utilised his firearm and his handcuffs as he did, was an abuse of trust that had been placed in him by the Queensland Police Service and the community at large."

She said if an ordinary member of the community had acted like this, a fine would not be adequate.

No conviction was recorded.

Appeal already filed

Queensland Police Union solicitor Calvin Gnech said an appeal against the conviction had already been filed.

"He is relieved this part of the process is over but his main priority at the moment is his welfare," he said.

Mr Gnech said once the appeal process was finalised, Flanagan would face police disciplinary proceedings.

He is currently receiving treatment for PTSD.