Yes! Once you start setting up your rewards, select “Limit availability” in the “Reward quantity” section. From here, you'll be able to set a limit for your rewards as well as a time period for their availability.
If you want to offer 20 VIP seats to your film's premiere, for example, you can limit the reward to 20. As soon as 20 people back the VIP premiere reward tier, it will be marked as sold out and other backers won't be able to select it.