Yes, but you can change it.
For Vms (
www.openvms.compaq.com) for example, when Decnet starts (before any other protocol like Tcpip, Lat, Lavc, Amds or any) it changes the Mac address from (for example 08-00-2B-.... to AA-00-04-00..., because it has the Decnet address in it.
A Decnet address of 3.2 means (3*1024)+2= 3074
In hex, this is 0C04, so the Mac address will be (reversed) aa-00-04-00-04-0C
See
http://h71000.www7.hp.com/wizard/wiz_4244.html
Regards