The short answer is "maybe".
The official documentation says:
Executes the specified delegate asynchronously with the specified arguments
which is pretty clear!
But... It goes on to say:
on the thread that the control's underlying handle was created on.
Which means that it does get executed asynchronously,
but only if the code it is executed on is not the UI thread.
So: "maybe".
Depends on exactly how that code is working on a wider context.