I am using Mikrotik RB951Ui-2HnD router in my office. What i want to ask you that i want to filter by MAC address so that to give permission for 5 pcs only. How can i give access to those 5 pcs only.

Not exactly a dude question, but you can do that with ip firewall, for example :

ip firewall filter add src-mac-address=01:02:03:04:05:06 action=accept chain=forward

Add rules for all macs that you need and then drop everything else.