Was I wrongly fired?

I was let go a week before my 90 day period was over. I was surprised because No manager never pulled me to the side and told me my performance was lacking in any areas, I have no write ups or warnings and I did what was asked of me. I have no progressive evaluations or anything. I always thought the 90 day period was to evaluate the employee and if he/she was lacking in any areas that was the period to improve it.