No, it's not, but the http://www.gamesas.com/topic/1386721-openmw-open-source-morrowind-thread-6/ team is working on putting Morrowind into a new engine which will run on Macs.
The OpenMW project is a community of fans who are creating a new open source engine for running Morrowind, the recipient of IGN's 2002 “RPG Game of the Year”. It is open source (GPL V3), cross platform (currently supporting OS X, Linux, and Windows), and written in pure C++. We are designing an engine that runs faster and is vastly more modifiable than the original game engine. We want to preserve Morrowind while also providing modders a better engine and tool kit for creating their works with