My dad is talking to himself? Is this normal?

My father, age 60, can be caught talking to himself many times throughout the day. he is usually zoning out and staring off at nothing. He usually talks to himself in a whisper and the words are indecipherable. Can be very scary especially when he's staring right at me while doing this and doesn't even realize. He has suffered from epilepsy, could this have something to do with it? Is it age? Or is it nothing to be worried about?