Yes. There are a variety of banks offering ATM machines. In the Playas del Coco area there are 7-8 machines available dispensing both US dollars and colones. You’ll generally pay between 0 and 1% exchange commission, plus flat fees of $1-3 per transaction.
Banks are generally open from 9 AM to 3 PM; a few have extended hours. You may need to be prepared for a wait, though; lines and bureaucracy can make getting money at banks an endeavor that requires a bit of time and patience. If you prefer not to carry a lot of colones, most international credit cards are widely accepted in Costa Rica, as are U.S. dollars.