I solved it with echo as below:
<?php if (is_page()) {
$cat=get_cat_ID($post->post_title); //use page title to get a category ID
$posts = get_posts ("cat=$cat&showposts=3");
if ($posts) {
foreach ($posts as $post):
setup_postdata($post); ?>
<div class="postlists"><div class="posttitle">
<a href="<?php echo get_permalink($post->ID); ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php echo $post->post_title; ?></a>
</div>
<?php the_excerpt() ?></div>
<?php endforeach;
}
}
?>