Ok, so it depends what you mean by desktop app. If you mean something that compiles Dart code to a native .exe or binary, and has bindings for things like QT, Swing or WPF, then no, you can't build a "desktop app" with Dart.
On the other hand, if your definition of a desktop app is an app that can be installed, has it's own icon on the desktop, runs independently of a web browser, then the answer is definately Yes - using Chrome Packaged Apps.
(The book, Dart in Action has a chapter dedicated to using Dart to build an "offline first" application, and installing it in Chrome. The Chrome Package App is the next step on from this).