Cat pacing in small degrees is perfectly normal. However, when the pacing moves from occasional into chronic behavior, it is possible there are underlying causes that should be examined.
In the wild, the big cats, such as lions and tigers, pace while seeking out food as well as when patrolling their territory. As cats became domesticated, the tendency to pace remained, especially at night, which is when cats do their best hunting.
It is possible that a cat is pacing because it is in pain. If the pacing behavior continues over a period of time, it is advisable to have a veterinarian examine the animal, especially if the pacing continues for more than a day.
Obsessive Compulsive Disorder (OCD) should be considered when looking at the pacing behavior. Any time a cat exhibits behavior that is unusual and prolonged, OCD should be considered. This can range from chronic vocalization (non-stop meowing) to persistent pacing.
If a cat is put outside whenever it begins to pace, it might learn that pacing will get it placed outside. This is called reinforced behavior. To break this behavior, the cat has to be kept inside when the pacing begins.
A female cat that has not been spayed will pace when she is in heat, compelled by biological imperatives. A male cat that has not been neutered will pace when it detects a nearby female in heat. Spaying and neutering will reduce the pacing behavior.