Our company have a lot of keyboard for desktop which have ps2 port at the rear. But I am using a notebook which only has usb port. I heard that not every keyboard can be converted to usb plug. Are both the type of converter and keyboard very important to determine whether one can convert a ps2 plug to usb plug?
There's two types of converters - active and passive. You use a passive converter if the keyboard supports USB and its just a matter of electrical conversion, else you use an active one .
Most reasonably modern (say in the last 10 years) keyboards SHOULD work with a passive converter, since they are designed to support both protocols.
I'd suggest trying a passive one first, then looking at an active one - geekhack has a periodically updated guide on active ps/2 to USB converters
EDIT: Since they are down...
The 'go to' active converter people recommend seems to be a generic model referred to as the blue cube
Other than the obvious (its blue, and a cube), they use a specific chip made by cypress and generally work.