Nope, once you've drawn something on a canvas there is no object to clear, just the pixels you've drawn. The clearRect method doesn't clear a previously drawn object, it just clears the pixels in the space defined by the parameters. You can use the clearRect method to clear the arc if you know a rectangle which contains it. This will of course clear any other pixels in the area, so you'll have to redraw them.

Edit: MooGoo has given a much better answer below