Hai friends here I am writing the code for creating a Custom validator for Radio button.
Please check it out and try.

Write a javascript function in .aspx page

function ValidateRadiobutton(oSrc, args)
if(document.getElementById("").checked ==

false&&document.getElementById("") .checked ==false)
args.IsValid = false;

Add custom validator

ClientValidationFunction="ValidateRadiobutton" runat="server"
ErrorMessage="Select Active/Inactive"
CssClass="ValidationMessage" ValidationGroup="status" Font-Bold="True" ForeColor="Lime">

Any doubts mail me at: radhekrsna@gmail.com