diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index 828be306fc..15a85d98f0 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -47,6 +47,7 @@ Yii Framework 2 Change Log
 - Bug #3817: `yii\rbac\PhpManager::getChildren()` returns null instead of expected empty array (qiangxue)
 - Bug #3843: Fixed Menu bug when using `template` with `encodeLabel` => false (creocoder, umneeq)
 - Bug #3863: Fixed incorrect js selector for `\yii\widgets\ActiveForm::errorSummaryCssClass` when it contains multiple classes (creocoder, umneeq)
+- Bug #3909: `Html::to()` should not prefix base URL to URLs that already contain scheme (qiangxue)
 - Bug: Fixed inconsistent return of `\yii\console\Application::runAction()` (samdark)
 - Bug: URL encoding for the route parameter added to `\yii\web\UrlManager` (klimov-paul)
 - Bug: Fixed the bug that requesting protected or private action methods would cause 500 error instead of 404 (qiangxue)
diff --git a/framework/helpers/BaseUrl.php b/framework/helpers/BaseUrl.php
index 1d0ca37a4e..e31c89d575 100644
--- a/framework/helpers/BaseUrl.php
+++ b/framework/helpers/BaseUrl.php
@@ -192,15 +192,19 @@ class BaseUrl
 
         if ($url === '') {
             $url = Yii::$app->getRequest()->getUrl();
-        } elseif ($url[0] !== '/' && $url[0] !== '#' && $url[0] !== '.' && strpos($url, '://') === false) {
-            $url = Yii::$app->getRequest()->getBaseUrl() . '/' . $url;
+        } else {
+            $hasScheme = ($pos = strpos($url, ':')) > 0 && ctype_alpha(substr($url, 0, $pos));
+            $char = $url[0];
+            if ($char !== '/' && $char !== '#' && $char !== '.' && !$hasScheme) {
+                $url = Yii::$app->getRequest()->getBaseUrl() . '/' . $url;
+            }
         }
 
         if ($scheme) {
-            if (strpos($url, '://') === false) {
+            if (empty($hasScheme)) {
                 $url = Yii::$app->getRequest()->getHostInfo() . '/' . ltrim($url, '/');
             }
-            if (is_string($scheme) && ($pos = strpos($url, '://')) !== false) {
+            if (is_string($scheme) && ($pos = strpos($url, ':')) !== false) {
                 $url = $scheme . substr($url, $pos);
             }
         }
diff --git a/tests/unit/framework/helpers/UrlTest.php b/tests/unit/framework/helpers/UrlTest.php
index a528c160b6..c98227ec04 100644
--- a/tests/unit/framework/helpers/UrlTest.php
+++ b/tests/unit/framework/helpers/UrlTest.php
@@ -115,6 +115,14 @@ class UrlTest extends TestCase
         \Yii::setAlias('@web4', '/test');
         \Yii::setAlias('@web5', '#test');
 
+        $this->assertEquals('/base/test/me1', Url::to('test/me1'));
+        $this->assertEquals('javascript:test/me1', Url::to('javascript:test/me1'));
+        $this->assertEquals('/base/java/script:test/me1', Url::to('java/script:test/me1'));
+        $this->assertEquals('#test/me1', Url::to('#test/me1'));
+        $this->assertEquals('.test/me1', Url::to('.test/me1'));
+        $this->assertEquals('http://example.com/base/test/me1', Url::to('test/me1', true));
+        $this->assertEquals('https://example.com/base/test/me1', Url::to('test/me1', 'https'));
+
         $this->assertEquals('http://test.example.com/test/me1', Url::to('@web1'));
         $this->assertEquals('http://test.example.com/test/me1', Url::to('@web1', true));
         $this->assertEquals('https://test.example.com/test/me1', Url::to('@web1', 'https'));