For Epicurus, ataraxia was the highest pleasure—not sensory indulgence but the absence of mental disturbance. He taught that we achieve this state by eliminating false beliefs, particularly irrational fears about death and the gods, and by living simply according to natural and necessary desires.
The Skeptics pursued ataraxia through suspension of judgment (epochē). By recognizing the equal validity of opposing arguments and abstaining from definite beliefs about non-evident matters, they found freedom from the anxiety of false certainty.
Ataraxia differs from apathy; it is not numbness but a condition of clear-minded serenity that allows one to engage with life fully while remaining unshaken by external circumstances. This ideal continues to influence contemporary approaches to peace of mind and stress reduction.
Source
Epicurean and Skeptical Philosophy