Yes,
there are mammals that lay eggs instead of giving birth to a live young. These mammals
are called Monotremes. One best example to this is the platypus and echidnas.
Platypus, which is also known as the duck-billed platypus, is a semiaquatic
egg laying mammal. Echidnas on the other hand are also called as spiny eaters.
Echidna and platypus are only the surviving members of the Tachyglosside. And are
the sole extant egg laying mammal
