Remove certain categories from the frontpage

I’m still not convinced that this is how you want to be doing this, but nevertheless the following will exclude posts of category 11 from showing up on the frontpage:

function exclude_category($query) {
	if ($query->is_home){
		$query->set('cat','-11');
		}
	return $query;
	}

add_filter ('pre_get_posts', 'exclude_category');

Paste the code into your theme’s functions.php.