No, he wasn't evil at first. But he was one of the first who turned evil.
In The Silmarillion, Sauron is described as a Maia of Aulë the Smith, named Mairon (which is not mentioned in The Silmarillion), meaning "the admirable." He wasn't as powerful as Valar but he was one of the most powerful Maiar.
At first, he was as Eru had created him: good and uncorrupt. His greatest virtue was his love of order and perfection, disliking anything wasteful. Dark Lord Morgoth took this as defect and corrupted him.
After allying himself with Morgoth, Mairon maintained his appearance of being faithful to the Valar, but secretly fed Morgoth information about their dealings.
Sauron during the First Age.
He was good at first. Dark Lord turned him evil.