If you're using the Text > Properties > Anchor Point, all you need to do is set the Text Alignment to Center. However, if you're talking about an "exact" center of the text, the easiest way to do that is to move the text to position 0,0 (center screen), drag down a guideline from the ruler and align it to 0 so you have a nice horizontal reference, then go into Text > Formatting and adjust the Baseline until the blue dots on either side line up with the guide (reset the tool to the regular transform tool if it's set to Anchor Point adjust).
As long as you don't change the text or the Anchor Point, the Anchor Point should stay where you set it.
If you need something more flexible, then use the Align To behavior and a "null" object (any object with its visibility turned off).