Town's January signing from Burton Albion will be back in goal for Oxford United's visit to Highbury because number one Alex Cairns is suspended after his red card in Saturday's defeat by Accrington Stanley.
O'Hara, who turns 26 next week, was preferred to Cairns for three games last month but the club stalwart has been back in goal for the last three.
And following confirmation that Cairns will be suspended for one game only, having been sent off for deliberately handling the ball outside the penalty area, he will be available for Monday's trip to relegation rivals Gillingham.
But team boss Stephen Crainey confirmed O'Hara has a golden opportunity to keep the shirt for both Easter games and beyond.
Town's head coach told The Gazette: “It's only one game for Alex, which is a bit of good news for us and that is the sort of competition I want.
“But Kieran is ready to play against Oxford and it's up to him now. If he deserves to keep the shirt he will.
“I'll pick the best team to win each individual match but if you play well you'll keep your place.”
Crainey hopes to have Anthony Pilkington available tomorrow after a tight hamstring saw the forward brought off at half-time against Stanley. “Anthony has done light training this week and we’ll wait on the medical department’s report before making a decision,” he added.