Yes, you might have to, especially during the holidays season. Due to a high demand for rental cars over this period, some rental companies might require a deposit to confirm your reservation.
This is a way to ensure that the confirmed reservation will be put to use. If you change your mind about your reservation and need to be reimbursed, please contact the rental company directly.
Please note that this is something different than the security deposit amount you are required to block on your credit card when you collect the car.