Get current URL inside ajax callback?
As said by @Jayendra Kainthola 
You need to store current path value in a session

$_SESSION['current_path'] = current_path();


Then use it inside your callback function as follows : 

function mymodule_ajax_callback($form, &amp;$form_state) {

$current_path = $_SESSION['current_path']  ;//gives the current path

}