First, be sure they are real pearls. While we usually think "akoya" when we see perfectly round pearls, imitations are also completely round.
Try rubbing 2 of the pearls together gently (after wiping them clean with a damp soft cloth, to remove grime.) Is it gritty feeling, or do they glide smoothly? Real pearls feel gritty; imitation pearls glide smoothly.
Edited to add: I have stopped recommending rubbing pearls against teeth. Teeth are harder than pearls and can scratch them.
Then, look at the clasp. Is it marked as gold, or gold colored base metal? Akoya pearls would not usually be strung with a base metal clasp.