McCarthy, whose side now sit four points and two places clear of the drop zone, felt the Tractor Boys were denied a clear penalty.
"How we haven't got a penalty is beyond me," he said.
"I'm not one for wearing rose-tinted glasses but there was a clear handball in the box and the referee has given nothing.
"We played well enough to win the game but we didn't put the ball in the net. The lack of goals is obviously a concern and it is something we work on every single day in training.
"But we would have scored twice had it not been for two fabulous saves. Peterborough's keeper has earned them their point.
"It's not a bad point for us either. It keeps us ticking over and keeps Peterborough below us."
- Sports & Recreation