function Start() {

	stage.addEventListener(MouseEvent.MOUSE_MOVE, CheckDirection);

}
Start();

var prevX=0;
var prevY=0;
var curX=0;
var curY=0;


var dirX:String="";
var dirY:String="";

function CheckDirection(e:MouseEvent) {


	trace("X movement: " + GetHorizontalDirection() + ", Y movement: " + GetVerticalDirection());

	e.updateAfterEvent();

}

function GetHorizontalDirection():String {

	prevX=curX;
	curX=stage.mouseX;

	if (prevX>curX) {

		dirX="left";

	} else if (prevX < curX) {

		dirX="right";

	} else {

		dirX="none";

	}

	return dirX;

}

function GetVerticalDirection():String {

	prevY=curY;
	curY=stage.mouseY;

	if (prevY>curY) {

		dirY="up";

	} else if (prevY < curY) {

		dirY="down";

	} else {

		dirY="none";

	}

	return dirY;

}

www.kirupa.com

Simple script to determine what direction the mouse is moving.

Detect direction mouse is moving

ActionScript 3