However, replays showed that he was in front of the last man when he received Pedro's pass before striking.
"It doesn't matter if it was offside. The ones that go on the scoreboard are the ones that count," Alba told reporters.
"It was a good bit of team play. Pedro picked me out fantastically, with his back-heel, which put me through and let me score with my right. I'm very happy with the goal.
"I'm happy with how things are going, and I'm always happy to score. I'm comfortable with Spain and with Barcelona."
Spain continue their qualification campaign on Tuesday when they host France in Madrid.