Fully liberated beings, e.g. arhants, can no longer create karma
that leads to samsara.
However, they still experience the ripening of old karmas.
Mogallana gets killed by bandits throwing rocks, Buddha gets
headache (due to being a fisherman hitting a fish with stone in
past lives) and eventually dies from eating poisonous food
(knowingly), etc.
However, even though they experience the effects of past karmas,
the effects are lessened very very much. As Buddha states in the
discourse on angulimala, the effects Angulimala would have to
endure for killing 999 people (he had to go to hell) had been
replaced with being ill-treated by people hurling things and
hurting him and not giving alms, etc. But he will not fall into
hell because he will no longer be reborn in samsara - he is an
arahant.