You can eat most dairy in moderation on keto. Be careful with milk, however, as it is rich in lactose, a type of milk sugar. Butter, cheese, cream and yogurt you can enjoy liberally unless you are lactose intolerant or have a milk protein allergy.
Be careful not to go overboard with dairy to avoid taking in more protein than necessary. There's a good reason why keto is a moderate-protein diet among other things - too much protein can kick you out of ketosis.