It should say AnyKey somewhere on it if it is.
It is almost only mechanical keyboards that do have NKRO.
First, it needs to have either diodes, or capacitive sensing, for all keys to be registered by the on-board microcontroller. Not all vintage mechanical keyboards do, but almost all modern mechanical do.
Then it needs to have either PS/2 or - a USB interface made for it.
Most modern mass-produced mechanical keyboards have only 6-key rollover (6KRO), being limited by using a simple USB interface.
Almost all custom DIY mechanical keyboards with TMK or QMK firmware do support full NKRO over USB, however.
NKRO (N-key rollover) means that
all keys can be registered at once. N = the number of keys on the keyboard.
6KRO means that all combinations of 6 keys are guaranteed to work, i.e. there is
at least one combination of 6+1 keys that
doesn't work. That doesn't mean that there can't be some combinations of 6+1 that
do work.
Most membrane keyboards are only 2KRO, but similarly support some combinations of more keys than just two.
(There are some manufacturers that claim 10KRO, 14KRO or even NKRO but which do not follow this definition above and therefore mislead customers ... Razer for instance)
BTW. PS/2 isn't actually that fast. That is a myth. Pretty much all PS/2 keyboards are slower than a modern gaming or custom keyboard with USB.