See WordPress SEO by Yoast: Hide Meta boxes in posts for non-admins

add_action(\'add_meta_boxes\', \'yoast_is_toast\', 99);
function yoast_is_toast(){
    //capability of \'manage_plugins\' equals admin, therefore if NOT administrator
    //hide the meta box from all other roles on the following \'post_type\' 
    //such as post, page, custom_post_type, etc
    if (!current_user_can(\'activate_plugins\')) {
        remove_meta_box(\'wpseo_meta\', \'post_type\', \'normal\');
    }
}