There’s those times where you don’t want a post from one of your categories appearing in your stream of posts in your homepage. It could be an unrelated post, a short, quick guide, or an announcement that you want hidden because it has to exist elsewhere. With just a little bit of code, you can remove what category you don’t want to appear in that stream. This technique is perfect to display only what you only want to show and hide those that aren’t required for your post.
Take a look at this simple code in this blog: http://wpmu.org/how-to-exclude-category-from-wordpress-homepage/