The simple answer is yes.

The legality of emulators was first established in 1982 when Coleco released an expansion module that allowed Colecovision owners to play Atari VCS (2600) games on their gaming system. Upon its release Atari immediately filed a lawsuit and sought an injunction against Coleco. In the end Coleco was found to have committed no copyright infringement and the module continued to be sold. In the late 90's Sony filed, not one, but three lawsuit against Bleem, a PlayStation emulator. The final ruling of Judge Charles Legge of the 9th U.S. District Court was that Bleem did not violate Sony's copyrights and the sales of Bleem continued.

Emulators can violate copyright laws when they are distributed with the original BIOS of a gaming system or computer (BIOS is an acronym for Basic Input Output System). Keep in mind that many emulators require a BIOS file to work but as long as the BIOS is not distributed with the emulator they are perfectly legal.