Nicholas Barker was in custody at Parklea Correctional Centre when the incident unfolded.

The 26-year-old was in the cafeteria area, when he was asked by one of the officers to return to his cell, about 1pm on November 3 last year.

According to court documents and captured on CCTV, Barker refused becoming aggressive and argumentative toward the prison officer, before walking off.

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The guard approached Barker to tell him again to go back to his cell, when Barker reached into his pocket and pulled out a sock that contained a tuna can and swung it at the guard's face.

The weapon missed, however when the prison officer tried restraining him, Barker swung it again and hit him in the back of the head, causing swelling.

Another officer saw the incident and rushed to help restrain Barker.

In Dubbo Local Court on Thursday Barker pleaded guilty to assaulting a law enforcement officer inflicting actual bodily harm.

The court heard Barker was in custody on remand for another matter, which he was later found not-guilty of.

Aboriginal Legal Service lawyer Tijana Caldwell said it was her client's first encounter with the prison officer, after being in quarantine for 42 days.

"He tells me he's ashamed and he feels he did act in an unacceptable way. He's very sorry and didn't mean to harm the guard," she said.

The court heard after this incident Barker was put in segregation for a month, and taken off 'buy-ups' for four months after this.

Buy-ups are a scheme which allows inmates to purchase additional items on a 'buy-ups' list using their wages or money deposited in their account by families and friends.

"I submit this punishment should be taken into account," Ms Caldwell said.

While Magistrate Theresa Hamilton took into account his young age, she said there appeared to be "no real reason" for the assault on the corrections officer.

"This is quite a serious assault in custody on an officer," she said.

The court heard Barker was not supported by his criminal history, and had received a number of terms of imprisonment for a number of assaults, including an assault on an officer and an assault occasioning actual bodily harm.

"So he has a very serious history for assaults," Magistrate Hamilton said.

"He seems to be on a revolving door in terms of imprisonment."

Magistrate Hamilton said however, a message must be sent that this behaviour toward a corrections officer is not tolerated.

Barker was convicted and sentenced to five months imprisonment.

However following his sentence, an appeal was lodged against the severity of the punishment. It will be heard in the Dubbo District Court on April 29.