That depends on which myth you're talking about! In Roman mythology, Mercury is a god of various things like commerce, travel, and trickery, and has a few different potential siblings.

* The most common version of Mercury's story makes him the son of Jupiter, the king of the gods, and Maia, a nymph. In this version, he has many half-siblings from Jupiter's other relationships, including Mars, Minerva, Apollo, Diana, Venus, Vulcan, and many others.

* Another myth suggests Mercury was the son of Jupiter and Maia's sister, Electra. This myth would make him the brother of Hermes, the Greek god of similar domains, and the half-brother of the other Olympians.

So, the answer is yes and no depending on the version you're looking at. He is always the son of Jupiter, but his mother and therefore siblings can differ depending on the source.