As the others said that is normally the case but nowadays most computers and mobiles have an option that randomize the MAC addresses on each connection.

These MAC addresses are known as locally-administered address. They look like this:

x2:xx:xx:xx:xx:xx
x6:xx:xx:xx:xx:xx
xA:xx:xx:xx:xx:xx
xE:xx:xx:xx:xx:xx

And rarely like this:

x3‑xx‑xx‑xx‑xx‑xx
x7‑xx‑xx‑xx‑xx‑xx
xB‑xx‑xx‑xx‑xx‑xx
xF‑xx‑xx‑xx‑xx‑xx