Validate Radio Button Group using Custom Validator and jQuery in ASP.Net

This way

  <asp:RadioButton ID="rnd_male" runat="server" Text="Male" GroupName="sex" CssClass="rnd" />
    <asp:RadioButton ID="rnd_female" runat="server" Text="Female" GroupName="sex" CssClass="rnd" />
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <script type = "text/javascript">
        function ValidateRadio(sender, args) {
            args.IsValid = $("[name=sex]:checked").length > 0;
        }
    </script>
    <asp:CustomValidator ID="CustomValidator1" runat="server" ErrorMessage="Gender is required" ClientValidationFunction = "ValidateRadio"></asp:CustomValidator>
    <asp:Button ID="Button1" runat="server" Text="Submit" />

No. It is not since here we are using Custom Validator and not RequiredFieldValidator.

If you want to clear message. Then use RadioButtonList and RequiredFieldValidator