A MAC address, or Media Access Control address, is a 48- or 64-bit address associated with a network adapter. While IP addresses are associated with software, MAC addresses are linked to the hardware of network adapters.
Since the MAC addressed are very rarely changed by default they are very interesting from security point of view. IP addresses can change dynamically, especially on networks using DHCP to assign IP addresses, so MAC addresses are often a more reliable way to identify senders and receivers of network traffic.
MAC address filtering is a common security measure to prevent unwanted network access on a wireless network. In MAC address filtering, a wireless router is configured to accept traffic from certain MAC addresses. In this way, as white listed devices are assigned new IP addresses through DHCP, they retain their ability to communicate on the network. Any intruder attempting to impersonate a valid user on the network by masquerading with a faked IP address will not be able to do so because the computer's MAC address will not match any of those in the white list. This security method is only minimally successful, however, as a determined intruder can fake a MAC address almost as easily as an IP address.
However this method is reasonably secure if the devices connected to the network are few and the attacker is not able to access the devices to find out their MAC address.MAC filtering is not a feature in 802.11 standard, its entirely a network layer filter which can be added on the AP itself.