Is it unusual for a cat to dig "for fun"?

I've never had an outdoor cat of my own. I recently started letting my cats go out into my privacy fenced in courtyard where there is some landscaping. This morning I saw my younger cat digging a hole. Other than it getting her all dirty I don't mind. I'd just never seen a cat digging like that. Is this a common cat behavior? I've known dogs to dig but I've never seen cats do it.