In many cases a dog might not mean anything, especially if you own a dog, then the reason you'd be dreaming of it is because you see your dog so often, but if you have a dream where you see a dog attack, dog biting you etc. then you need to look into this deeper because these symbols are not meaningless.
If you have a dream of a dog attack then this means that you are worried about backlash for something that you have done recently. This makes more sense of the dog in question is a familiar dog to you. A dog will attack only if you have harmed it greatly or if you do not know it and it is a naturally aggressive dong. What type of dog this is in your dream matters greatly to interpretation. If the dog in your dream that is attacking you or giving you a dog bite is one that you do know in real life and one that you shouldn't be afraid of then this means that you have done something to anger someone else that you know and it will cause them to be very angry with you. A dog attack, dog bite, dog biting hand etc is nothing to laugh about, especially if it is a familiar dog.