EA has announced an alpha version of the Origin client for Mac is available for testing to a limited number of users in the US and UK. Origin for Mac will eventually evolve, offering a similar experience for Mac users as already seen on PC. In its current form, however, the Mac client does not include the ability to stream gameplay directly to Twitch or purchase software. According to the Origin FAQ, those features will be added soon.
Origin for Mac requires OS X 10.6.8 or newer, with an Intel Core Duo 2 processor or better.