(Can and block)

1. Setting the class of the menu item(WP)

//setting the class of the menu item

add_filter('nav_menu_css_class' , 'special_nav_class' , 10 , 2);

function special_nav_class($classes){
     if(is_page(4)){
             $classes[] = 'active';
     }
     return $classes;
}

2. Setting the class of the menu item( another way)

//We make each menu active
class Custom_Walker_Nav_Menu_top extends Walker_Nav_Menu
{
    function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
        $is_current_item = '';
        if(array_search('current-menu-item', $item->classes) != 0)
        {
            $is_current_item = ' class="active"';
        }
        echo '<li'.$is_current_item.'><a href="'.$item->url.'">'.$item->title;
    }

    function end_el( &$output, $item, $depth = 0, $args = array() ) {
        echo '</a></li>';
    }
}