Birmingham needed a late goal from Chris Burke to deny Barnsley their second win of the season.
Jacob Butterfield gave the visitors the lead from 30 yards out after 33 minutes, his second goal this campaign.
But with just four minutes remaining, Burke, a summer signing from Cardiff City, struck from 25 yards for his first goal for Blues.
The home side could have gone on to sneak a win but Marlon King's late shot hit the inside of the post.
It would have been harsh on the visitors, who deserved their half-time lead after dominating the opening 45 minutes.
Butterfield's strike made him the first visiting player to score at St Andrews' in the league this season - and the point saw Blues lose their 100% home record.
There were injury scares for both sides as Curtis Davies was stretchered off after just nine minutes for the home side with a knee injury, before Matt Done was forced off 20 minutes later for the visitors.