hossein.rahimi on "popular posts"

Hi
I am using this code to display popular posts on single posts:

<div class="top_app">
<h5>محبوب ترین ها نرم افزار ها ، بازی ها</h5>
</div><!--top_app-->
<div class="scroller">
    <ul id="mycarousel" class="jcarousel-skin-tango">
	<?php

$my_query = new WP_Query('orderby=comment_count&showposts=12');
while ($my_query->have_posts()):
$my_query->the_post();
$do_not_duplicate = $post->ID;?>
        <li>
		<?php
$thumb = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'popular-thumb' );
$url = $thumb['0'];
?><a href="<?php the_permalink() ?>"><img src="<?php echo $url; ?>" width="84" height="92" alt=""  title="<?php the_title(); ?>"></a></li><?php endwhile; ?>
    </ul>
</div><!--scroller-->

how I filter this list with category of posts?