You may not be able to see mites with the naked eye. A vet can take a skin scraping or use tape to possibly get a sample and examine it under the microscope. I think it would be wise to take him in to be examined.

Could it be a normal molt? Some buns molt in patches. They look moth-eaten, but it’s normal. After a week or so new hair (like fine velvet) starts to show on the bald patches. Bunnies can molt in patches one time and more gradually at other times, I’ve found with my buns.

Since there’s no “dandruff” or flakes or scabs on the bare skin, this sounds more like a molt than mites to me. Mites often start att the nape of the neck/between the shoulder-blades and work their way outwards in a triangular pattern.

Rabbits can carry mites from when they are very young, that’s probably the most common “cause” of mites. They get a few mites from their mother, the mites can’t multiply very much, sth stressful happens to the rabbit and the immune-defense can’t keep the mite-number down. This is very common. The stress doesn’t have to be severe, so it’s not like it’d absolutely have to be sth you’d have noticed.

If you still fear it’s mites, you can ask your vet for a prescription for Revolution (selamectin). It’s bunny safe and highly effective against several types of parasites. Whatever you do, NEVER use any compound containing Fipronil on a rabbit. It’s sold as Frontline and Sentry and Effipro and probably other names as well. I’m just saying this because we always warn bunny-owners about Fipronil when parasites are suspected – it’s so easy to buy OTC and it’s good for cats and dogs, but it’s really lethal to rabbits.

ETA: If this is indeed a molt, you should take extra care to brush him/pluck out tufts of hair with your fingers. When the hair comes off in clumps, there’s a big risk the bunny ingests too much of it when he grooms himself. Too much hair isn’t good for the tummy. 

Keep an eye out for flakes and crusts and of course, “desperate” attempts at grooming himself where he can’t reach (that would indicate itching.)

My Bam sometimes molts in patches on his back. Sometimes he doesn’t. He’s very inconsistent.