Попробуй так:
Код AS3:
<mx:HTML id="myhtml" x="0" y="0" width="100%" height="100%" location="http://localhost/test.html" htmlDOMInitialize="makeListeners();"/>
private function makeListeners():void {
var body:Object = myhtml.domWindow.document.body;
body.addEventListener("mousemove", onMouseMove, true);
}
private function onMouseMove(evt:MouseEvent):void {
trace(evt.target.innerHTML);
}