I recently got a macbook air and all of a sudden my iMessages are going there rather than to my phone?

I got a macbook air four days ago. I texted my friend to ask her address and my roommate to ask a question. I never got an answer back, until I looked at my laptop at night to see that their responses were in the messages app on my dock. I don't know why it is doing that, I mean they are under the same id but why would one get it and not the other?