How do I make a button's overstate trigger from keyboard detection?

programming flash
1 
stage.addEventListener(KeyboardEvent.KEY_DOWN, checkKeys)

function checkKeys(event:KeyboardEvent):void {
	if(event.keyCode == 48) {
		zero_mc.gotoAndPlay(2);
	}

}

zero_btn.addEventListener(MouseEvent.CLICK, launchZero);
function launchZero(event:MouseEvent):void {
	zero_mc.gotoAndPlay(2);
}

When I press the ‘0’ key it makes the movie play. When I click the actual button it also makes the movie play. But how do I make it so that when I type ‘0’ the overstate of the button becomes activated? In this way keyboard detection and mouse_down would work together.

Thanks for any help.