Random Post on Search Page

Please Help I have some question, I tried to create Random Post on Search Page. I was tried to displayed 5 random post only. But when I check it on my search page. The Result displayed more than 30 post

<div>
<?php
      $random_query = new WP_Query(array(
      'post__not_in' => $do_not_duplicate,
      'showposts' => 5,
      'orderby' => 'rand'
      ));
      while ($random_query->have_posts()) : $random_query->the_post(); ?>
<a href="<?php the_permalink() ?>"><?php the_title();?></a>
    <?php endwhile; ?>
</div>

How To fix it?

Best Regards

Jauhari