SVG, 177 bytes

<svg><g transform=translate(75,75)><circle id=x r=.5 cx=56 fill=#800080><animateTransform xlink:href=#x attributeName=transform type=rotate to=360 dur=60s repeatCount=indefinite

Invalid markup from hell to breakfast, but it runs (in Chrome at least). Like a HTML5 canvas, the default size for an SVG appears to be 300x150, so that's what this is assuming.

Edit: Whoops, I'd accidentally left in a duration of 6 instead of 60. Fixed that, but also found that 0.5 works as just .5, so no change in the byte count.