Could be caused by a number of things, from a medical condition to an everyday object.
Vitamin deficiency (such as Vit B12) can show itself by tongue tingling, as can an STD (if you've been a bit naughty with someone nasty!)
It might even be something as simple as something which you've touched before putting your fingers in your mouth - if say, you bite your nails or lick your finger before turning over a page.
Make a note of when it happens / how often etc, and what you were doing just beforehand.
In any case, you should get yourself checked out by a GP, just to be safe. It could be something he or she can sort for you there and then.