Isolate AP connected to via the same ethernet port?

Look at this example for Router…
http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1

The first example has a router config file which kinda shows what you need.

This next link includes an example of a MT device just being used as an AP/Switch.
https://forum.mikrotik.com/viewtopic.php?t=182276