/* The Number 611 is my category ID number. Please replace this with your own! 
           Add this snippet to your functions.php file. */

        function exclude_cat($query) {
		if ( $query->is_home) {
			$query-> set('cat','-611');
		}
		return $query;
	}

	add_filter('pre_get_posts','exclude_cat');

http://www.brettwidmann.com/2011/12/filter-categories-wordpress-blog/

Ever want to filter out a category from your blog page. Here's how you do it! Just add this snippet to your functions.php file.

Filter Category from WordPress Blog Page

wordpress

PHP