Beavers are related to some Old World rodents, such as the Norway rat and house mouse, as well as to some New world species such as the deermouse and muskrat, but since it branched off really early, before deer mice and muskrats and Norway rats evolved from a common ancestor, it is therefore equally close to the deer mouse, Norway rat, house mouse and muskrat and it is not possible to say whether it is more closely related to one of these species vs. others.
