aravinth I assume this is a signup using a social account? Does normal signup with password work?
Maybe there's an incompatibility between social login and/or terms extension and/or recaptcha extension.
If this happens for every attempt, you could try disabling one of these 3 extensions and see if the issue still happens.
Also make sure registration is still open under Permissions. Registrations must be turned on to allow new users to register with social as well.