Although hyenas have a rather dog-like appearance and live in large groups as many wild dogs do, they are not classified as dogs. Hyenas are actually members of a group called the Feliformia and are more closely related to cats than to dogs.
There are two main subgroupings of the order Carnivoria, the scientific classification that all modern mammalian predators fall under: Feliformia and Caniformia. Feliformia, which hyenas belong to, is a broad group that includes the mongoose and fossa as well as the many species of cats. Within Feliformia, hyenas form their own group, called Hyaenidae, completely separate from cats and other Feliformia members. They can be thought of as cousins to cats and other members of the group rather than being directly related. Hyenas are neither dogs nor cats, but they are more like cats in terms of ancestry and anatomy than they are like dogs.