Is it common for my father to walk around the house a lot?

Yes, restless pacing by someone with dementia is a common behavior. It's a form of wandering, the most extreme example of which is leaving the house without telling anyone, or wandering off in public. Sometimes frustration, stress, or anxiety can lead to an increase in restless movements. Or perhaps your dad is bored and doesn't feel engaged with an activity. You can read more about what triggers wandering and what to do about it here.