It depends if its owned or leased. If it is a leased receiver, you will have to fulfill a commitment. If it is owned, you don't have any additional commitment. When you activate it, be sure to confirm they set it up as owned w/o a commitment.
Before you buy it, make sure to get the RID and talk to DirecTV to confirm that you would be able to activate the box if you get it. They can also tell you if its owned or leased.
Your welcome! One last thing, I was assuming you are already a DirecTV customer and just adding a receiver. If you are new a customer, when you start service I believe you will have a commitment, leased or owned. Also, didn't you already ask this a few months ago?