Antonyms of nervous:
untroubled, relaxed, unexcitable, unexcited, confident, self-assured, self-confident, sure, controlled, self-controlled, calm, collected, cool, easy, happy-go-lucky, nerveless, restful, pacific, calming, comfortable, peaceful, quiet, quieting, tranquil, serene, easygoing, laid-back, imperturbable, unflappable, unshakable.
Examples of usage:
  1. " But you're on the ground now, Lem," said Columbine, with a nervous laugh.
    "The Mysterious Rider", Zane Grey.
  2. Mentally she complained of being nervous and easily awakened at night; consciousness was clear; she was well oriented; no hallucinations or delusions could be elicited.
    "Studies in Forensic Psychiatry", Bernard Glueck.
  3. Don't stand there and watch me, please; you make me nervous.
    "Brother and Sister", Josephine Lawrence.