Hi SUJAYS,
Check this example. Now please take its reference and correct your code.
HTML
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.7.8/angular.min.js"></script>
<script type="text/javascript">
var app = angular.module('MyApp', []);
</script>
</head>
<body>
<form id="form1" runat="server">
<div ng-app="MyApp">
<asp:TextBox ID="txtempname" runat="server" ng-model="Name"></asp:TextBox>
<span ng-show="!Name" style="color: Red;">Name required!</span>
</div>
</form>
</body>
</html>
Screenshot