Due to some reasons (like don’t allow to enter chars in Price TextBox), we restrict users to enter chars in TextBox. We can implement this functionality by using below method.

 <script type="text/javascript">
 function checkNumeric(event) {
var kCode = event.keyCode || event.charCode; // for cross browser check

//FF and Safari use e.charCode, while IE use e.keyCode that returns the ASCII value 
if ((kCode > 57 || kCode < 48) && (kCode != 46 && kCode != 45)) {
//code for IE
 if (window.ActiveXObject) {
 event.keyCode = 0
 return false;
 }
else
{
 event.charCode= 0
}
 }
}
</script>

<asp:TextBox ID="TextBox1" runat="server" onkeypress="return checkNumeric(event); ></asp:TextBox>