Acturally this happens all the times. Normally users can configure more than one IP address on one NIC but one IP address can only be allocated to one NIC. For example, you can add many IP address to specify yourself and even more than one gateway in Microsoft Windows OS, advanced TCP/IP settings.
Another scenaro, if there any virtual machine hosted in your system, and they are bridged to the physical NIC, They will consequently be exposed to the network, and some virtual machine use multiple IP address over a single MAC address.