This generally happens from when you clicked play on a Mixcloud embedded mix on Facebook and missed the sign that asked you for your approval to create the account.
All you need to do now to delete the account is, going to www.mixcloud.com, click on Login with Facebook and then go to your account settings to delete it. For more information on how to do this, see our article here.
Please note, for security reasons, only the account owner can delete an account and that once an account has been deleted is impossible to bring it back.