Posh were indebted to goalkeeper Bobby Olejnik as he produced several fine saves to blunt the Town attack.
Olejnik brilliantly kept out Frank Nouble in the first half before making an even better stop to claw out a David McGoldrick header in the second period.
"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," said McCarthy.
"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."
McCarthy, whose side are four points and two places clear of the drop zone, also felt his side should have had a late 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."