Have you read Migrating to WebView in Android 4.4: http://developer.android.com/guide/webapps/migrating.html
Blockquote If you call methods on WebView from any thread other than your app's UI thread, it can cause unexpected results. For example, if your app uses multiple threads, you can use the runOnUiThread() method to ensure your code executes on the UI thread:
runOnUiThread(new Runnable() {
@Override
public void run() {
// Code for WebView goes here
}
});