Body's response to meditation
That's not all that uncommon.  If it's not your toes, it'll be something else.  Personally, my hands will sometimes contract by themselves and my forearms will occasionally rotate a few degrees.  Other people usually report muscles in their faces that start to fire, maybe their shoulders will bounce a bit, etc.

All this is a result of tension leaving the body.  The more you relax into your meditation, the more your body will loosen up.  The deeper the concentration, the more relaxed you'll get.  As you keep at your practice, you might even see other places start to loosen up - places of deep seated tension that you didn't even know existed.

It's nothing to be alarmed about if that's your concern.