You are getting the macs - Media Access Control - of two different bits of hardware.
Your machines are invariably going to be connected via a switch connected to a router. The address you get from the machine is the mac of the network card or chip on the machine / laptop.
Other mac is the one which your router returns having pinged an address assigned by the router?
Or do you have more than one network adaptor? If you have a wireless access card as well as the LAN card for example.
"some computers have more than one MAC address. This is because MAC addresses are attached physically to the network adapter hardware and not to the base computer itself. Computers with multiple network adapters installed (sometimes called multihomed systems) therefore possess multiple unique MAC addresses."
"In some exceptional situations a single interface can have two MAC addresses, however this happens only if using something like a virtual mahine, where the virtual computer needs to share your ethernet port. To make sure that the packets go to the right place, the virtual machine will create its own MAC address."