Lee Tomlin gave the Posh a 17th minute lead but Charlie Austin equalised for the Robins from the penalty spot 18 minutes from time after Mark Little had brought down Matt Ritchie.
Johnson told BBC Sport: "I think it was a fair result. We had our opportunities in the first half and they had theirs in the second.
"First half I thought we played some really good football and deserved to be coming in 1-0 up but for some reason we didn't quite see it through. Swindon have beaten some good teams at home so a draw is a good result."
On a possible replacement for striker Aaron Mclean, who looks like sealing a switch to Hull City as soon as the January transfer window opens, he added: "We'll bring someone in if the right person becomes available and we're looking at a couple of options.
"If not then Tommo (Lee Tomlin) has shown us that he can be a match for anyone in that hole behind the striker. He showed some great touches and he sees openings."
Source: PA
Source: PA