This Conditional Tag checks if page being displayed is "paged" and the current page number is greater than one. This is a boolean function, meaning it returns either TRUE or FALSE.
Note: This refers to an archive or the main page being split up over several pages, this does not refer to a Post or Page whose content has been divided into pages using the <!--nextpage--> QuickTag.
<?php is_paged(); ?>
This tag does not accept any parameters.
If you need to check which page of the blog you are on, you can look in $wp_query->query_vars['paged']. Remember that inside functions you might have to global $wp_query first.
is_paged() is located in wp-includes/query.php
.