Mikrotik['noob'] - Is there a way to block a specific device from accessing my LAN using their MAC address?

Hi,

I have some Mikrotik switches, with some wireless access points. I've noticed that there is an unknown device attached to the network. I would like to block that device from acces the network. Is this possible and if so, how is it done?

Everything i've come across seems to be about restricting devices from accessing the internet. When i tried a filter out, i blocked all devices from the network. Ops!

I know that the ideal scenerio would be to change to wireless password, but i would also like to block the device specifically too. I know how to easily do this on a domestic router, but a commerical router like this seems to have me stumped a little.

The device i'm attempting to apply the filter/block is a RB750Gr2 which controls the access points and is the gateway device to the internet.