exclude post according to assigned category WordPress

I have this code that shows the most viewed publications, I would like to exclude the entries assigned to a specific category, for example the ID of the category I want to exclude is "4"

  <div style="text-align:center;margin-top:4px">          <?php $  my_query = new WP_Query('meta_key=post_views_count&orderby=meta_value_num&order=DESC&showposts=6&ignore_sticky_posts=1'); while ($  my_query->have_posts()) : $  my_query->the_post(); $  do_not_duplicate = $  post->ID; ?>         <div class="recomend-posts">         <a href="<?php the_permalink(); ?>" title="<?php the_title(); ?> (<?php $  values = get_post_custom_values("Year"); echo $  values[0]; ?>) online">             <?php if ( has_post_thumbnail() ) {?>                 <?php the_post_thumbnail('index-thumbnail');?>             <?php }else{ ?>                 <img src="<?php bloginfo('template_url');?>/images/no-image.jpg" alt="<?php the_title();?>" />             <?php }?>         </a>     </div>         <?php endwhile; wp_reset_query(); ?>         </div> 

any ideas? thanks