I have noticed that when using
actionBar.setSelectedNavigationItem(x)
in the onCreate() method of my Activity, the tab item at position 0
For any others looking to do this you can also set the tab to selected by setting the position and then set true or false to indicate which tab should be selected
actionBar.addTab(tab1, 0, false);
actionBar.addTab(tab2, 1, true);
actionBar.addTab(tab3, 2, false);
Here are the docs on this approach: http://developer.android.com/reference/android/app/ActionBar.html#addTab(android.app.ActionBar.Tab, int, boolean)