test if display = none

If you want to get the visible tbody elements, you could do this:

$('tbody:visible').highlight(myArray[i]);

It looks similar to the answer that Agent_9191 gave, but this one removes the space from the selector, which makes it selects the visible tbody elements instead of the visible descendants.

EDIT:

If you specifically wanted to use a test on the display CSS property of the tbody elements, you could do this:

$('tbody').filter(function() {
     return $(this).css('display') != 'none';
}).highlight(myArray[i]);