I agree with
kno4te
that it could be a bit of small fungus.
However... I have a flowerhorn x parrot hybrid that had the exact same thing happen. I dosed the water and kept a
vigilant eye on it, and when the spot continued to grow in size and get red around the edges, I immediately knew it was
HITH disease (hole-in-the-head). Even though she (my fish) didn't display any odd behavior, she did stop eating. Thankfully, I caught it early enough and did one round of dosage with
API General Cure and like magic, the "white scab" disappeared. She began getting her voracious appetite back and is even playful again. So...
Just monitor your fish vigilantly. If you start to notice that the spot on it's head is growing, getting fuzzy-looking, and it starts to refuse food or behave differently than normal, you'll know! Good luck and i hope your fish pulls through it!