if( !function_exists( 'marstheme_excluding_the_category_on_homepage' ) ){
    function marstheme_excluding_the_category_on_homepage( $query ) {
        if ( $query->is_home() && $query->is_main_query() ) {
            $category_id = ''; // change your category id here.
            $query->set( 'category__not_in', array( $category_id ) );
        }
    }
    add_action( 'pre_get_posts' , 'marstheme_excluding_the_category_on_homepage', 10, 1);
}