Iain Vigurs had cancelled out Anthony Stokes' opener when Celtic forward Tony Watt swept home Dylan McGeouch's cross from six yards but the assistant referee had his flag raised.
Mjallby said: "We played a good first half and it was very annoying to concede a goal late again in the first half and then we should have had a goal allowed.
"I have seen it on television and it clearly wasn't offside. It would have been nice to go in at half-time with a lead.
"It was more annoying to concede a late goal in the first half because we were playing well.
"We lost a goal out of nothing although, overall, we defended much better and kept our shape.
"The second half wasn't that great, we didn't create that much and went a bit too deep because they had the wind behind them."
Celtic had some first-half success with a 4-3-3 formation but a strong wind exacerbated the problems caused by a bobbly pitch in Dingwall.
"It is hard to play football on that pitch," Mjallby added. "It was dreadful.
"We had to go a bit more direct and that didn't suit us. It was more of a physical battle although a draw was a fair result.
"The pitch is equal for both teams but the way we play football it doesn't suit. It is bobbly and there is no grass but it was quite soft and it was not dangerous."