Edit in JSFiddle

$(document).ready(function(){ 
   $("#block").mousemove(
	
	function (pos) {  
	$("#floatingmes").show(); 
    $("#floatingmes").css('left',(pos.pageX+10)+'px').css('top',(pos.pageY+10)+'px'); 	
    }   
   
   ).mouseleave(function() {
    $("#floatingmes").hide();  
}); 
   
   

}); 
<div id="floatingmes">Подсказка</div>

<div id="block"></div>
#floatingmes {position:absolute; z-index:999; top:0; left:0; width:100px; background:#FFF; opacity:0.85; border:1px solid #000;}

#block {width:500px; height:500px; background:#900;}