<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/07/16/disabling-keyboard-navigation-on-the-combobox-control-in-flex/ -->
<mx:ComboBox xmlns:mx="http://www.adobe.com/2006/mxml">
    
    <mx:Script>
        <![CDATA[
            override protected function keyDownHandler(event:KeyboardEvent):void {
                // ignore
            }
        ]]>
    </mx:Script>
    
</mx:ComboBox>