<script type="text/javascript">
    var urls = ["http://google.com","http://yahoo.com","http://apple.com","http://google.com"];
    setInterval(function() {
        var rand = Math.floor(Math.random()*urls.length);
        //alert(rand);
        document.getElementById('myiframe').src = urls[rand];
    }, 5000);
    </script>
<iframe id="myiframe" src="http://google.com" id="myFrame" width = "300" height= "250"></iframe>