Has your bun been out in the dirt lately? Dirt can carry the ticks. You should take your rabbit to a vet for treatment, for ticks can give health issues to your rabbit. Groom your bun daily, if you come across a tick, remove it with some tweezers. Try to get rid of them before the ticks have had their fill, in some cases rabbits get anemia. Ticks can also pass on muscle weakness to your bun, if you notice his legs getting weaker, this could suggest that the tick is passing on an infection, to your bun.
Ticks prefer on the ears and between them, on the face, and the legs. If your rabbit realizes he has ticks, then he will sometimes try to pick them off himself. In which case, it may pop or burst, leading to your rabbit inhaling or consuming infected blood, or he might take half tick and leave the rest, which makes infection possible. And/or if he swallows the tick, he may become unwell. Vets do have a special medicine for ticks, and our vet recommends if you buy over-the-counter medicine, make sure it’s rabbit friendly because some that are made for other animals can cause harm to rabbits.
Here’s a website that might help https://www.rabbitcaretips.com/how-to-treat-ticks-in-rabbits/
I wish you the best of luck!