It's not unusual for there to be a bald spot under a scab. The hair should grow back in as the skin heals. It does bear watching, though, to see if the bald spot spreads or see if there's an irritation there that will result in another scab. If it seems to be a recurring problem, consulting your vet would be a good idea.
Welcome to the board--and we'd love to see the rest of your dog if you have some pics to share!