diff --git a/packages/docusaurus-theme-classic/src/theme/NavbarItem/DropdownNavbarItem.tsx b/packages/docusaurus-theme-classic/src/theme/NavbarItem/DropdownNavbarItem.tsx
index b8ab9d7cd5..7dec9776e9 100644
--- a/packages/docusaurus-theme-classic/src/theme/NavbarItem/DropdownNavbarItem.tsx
+++ b/packages/docusaurus-theme-classic/src/theme/NavbarItem/DropdownNavbarItem.tsx
@@ -7,21 +7,49 @@
 
 import React, {useState, useRef, useEffect} from 'react';
 import clsx from 'clsx';
-import {useLocation} from '@docusaurus/router';
 import {
   isSamePath,
   useCollapsible,
   Collapsible,
+  useLocalPathname,
 } from '@docusaurus/theme-common';
 import type {
   DesktopOrMobileNavBarItemProps,
   Props,
 } from '@theme/NavbarItem/DropdownNavbarItem';
+import type {LinkLikeNavbarItemProps} from '@theme/NavbarItem';
+
 import {NavLink} from '@theme/NavbarItem/DefaultNavbarItem';
 import NavbarItem from '@theme/NavbarItem';
 
 const dropdownLinkActiveClass = 'dropdown__link--active';
 
+function isItemActive(
+  item: LinkLikeNavbarItemProps,
+  localPathname: string,
+): boolean {
+  if (isSamePath(item.to, localPathname)) {
+    return true;
+  }
+  if (
+    item.activeBaseRegex &&
+    new RegExp(item.activeBaseRegex).test(localPathname)
+  ) {
+    return true;
+  }
+  if (item.activeBasePath && localPathname.startsWith(item.activeBasePath)) {
+    return true;
+  }
+  return false;
+}
+
+function containsActiveItems(
+  items: readonly LinkLikeNavbarItemProps[],
+  localPathname: string,
+): boolean {
+  return items.some((item) => isItemActive(item, localPathname));
+}
+
 function DropdownNavbarItemDesktop({
   items,
   position,
@@ -102,12 +130,20 @@ function DropdownNavbarItemMobile({
   position: _position, // Need to destructure position from props so that it doesn't get passed on.
   ...props
 }: DesktopOrMobileNavBarItemProps) {
-  const {pathname} = useLocation();
-  const {collapsed, toggleCollapsed} = useCollapsible({
-    initialState: () =>
-      !items?.some((item) => isSamePath(item.to, pathname)) ?? true,
+  const localPathname = useLocalPathname();
+  const containsActive = containsActiveItems(items, localPathname);
+
+  const {collapsed, toggleCollapsed, setCollapsed} = useCollapsible({
+    initialState: () => !containsActive,
   });
 
+  // Expand/collapse if any item active after a navigation
+  useEffect(() => {
+    if (containsActive) {
+      setCollapsed(!containsActive);
+    }
+  }, [localPathname, containsActive]);
+
   return (
     <li
       className={clsx('menu__list-item', {
diff --git a/packages/docusaurus-theme-common/src/index.ts b/packages/docusaurus-theme-common/src/index.ts
index 32010abaff..f22920beb0 100644
--- a/packages/docusaurus-theme-common/src/index.ts
+++ b/packages/docusaurus-theme-common/src/index.ts
@@ -63,3 +63,5 @@ export {
   AnnouncementBarProvider,
   useAnnouncementBar,
 } from './utils/announcementBarUtils';
+
+export {useLocalPathname} from './utils/useLocalPathname';
diff --git a/packages/docusaurus-theme-common/src/utils/useLocalPathname.ts b/packages/docusaurus-theme-common/src/utils/useLocalPathname.ts
new file mode 100644
index 0000000000..8e16158242
--- /dev/null
+++ b/packages/docusaurus-theme-common/src/utils/useLocalPathname.ts
@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import useDocusaurusContext from '@docusaurus/useDocusaurusContext';
+import {useLocation} from '@docusaurus/router';
+
+// Get the pathname of current route, without the optional site baseUrl
+// - /docs/myDoc => /docs/myDoc
+// - /baseUrl/docs/myDoc => /docs/myDoc
+export function useLocalPathname(): string {
+  const {
+    siteConfig: {baseUrl},
+  } = useDocusaurusContext();
+  const {pathname} = useLocation();
+  return pathname.replace(baseUrl, '/');
+}