Animate the offset value. Just set a couple of keyframes. Your timeline should look something like this:

Pay attention to the stroke and offset properties.
You could also add an expression like this to Offset:
time * 400
If you want to reverse the direction you'll run into trouble with big negative numbers so start out with a big positive number like 6000 for the first and then something like 100 for the last. If you are using the expression to get it to move counter clockwise use this expression:
6000 - time * 400
The larger the last number the faster the movement.