Substitute Jamie Vardy struck home from close range after good work from David Nugent in the 90th minute to seal a 2-2 draw after the the Tykes had led 2-1 at the interval.
The Foxes, who had scored 10 goals in the previous two home games, took the lead in the eighth minute through Anthony Knockaert but then gifted Barnsley two goals with poor defending. Stephen Dawson scored in the 26th minute and Reuben Noble-Lazarus fired them in front 12 minutes later.
A shock result looked on the cards until Vardy's late strike and while Pearson was glad to come away with a share of the spoils he was frustrated Leicester could not claim all three points.
"I didn't think Barnsley were ever in the game, but we gifted them two goals and then had to fight very hard to get something out of it," he said.
"We could have had a penalty at the end for handball, but I don't blame the officials for us not getting three points.We've not been ruthless enough really.
"We had plenty of chances but did not play as well as we can do. We started the game well but then gave them two goals out of nothing. That was disappointing but we got something out of the game and that has got to be a positive. But we've got to win those sort of games.
"Right through the second half they were never a threat, and we were probably as dominant as you can be without winning the game. But it just shows you that you cannot afford to give those sort of goals away. They were just poor goals.
"When you play a side who get as many players behind the ball as they do, it gives them something to hang on to. We exerted a lot of pressure in the second half but it never really happened for us until the late equaliser.
"I was pleased for Jamie Vardy because he has had a spell where he has not been scoring."