A DOG that had already been classified as "menacing" has attacked another dog in a "frightening" incident.

Byron Shire Council's legal services coordinator, Ralph James, said the dog's owner has been convicted of being in charge of a menacing dog, and ordered to pay the council's legal costs and a fine, totalling $1500.

Mr James said the attack happened near the Federal Hall just before 8.30am on August 15.

The dog, an American Staffordshire terrier, was unrestrained when it attacked a spoodle which was being walked on a leash. It bit the spoodle on the ear, neck and back.

"The court at Mullumbimby heard the attacking dog was not secured on a leash nor was it wearing a muzzle," Mr James said.

"This animal is known to Byron Shire Council as it was declared 'menacing' in 2014, and this means the owner is required to muzzle the dog, keep it on a leash when in public places and ensure it is in the control of a responsible adult.

"It was a frightening incident for the other person involved and it's important for people to know there are very harsh penalties in place for the owners of dogs who are menacing and dangerous.

"Aside from paying the council's legal costs and a fine, the defendant also has to pay a $450 vet bill for the injured spoodle.

"The maximum penalties for dog-related offences under the Companion Animals Act is a fine of up to $70,000 and a gaol term of up to five years."