Jens Keller's side had arguably the better of the opportunities at the Veltins Arena, with Max Meyer and Kevin-Prince Boateng almost breaking the deadlock for the Gelschenkirchen outfit.
But Thomas Tuchel's men played their part in a lively encounter, particularly showing promise in the first half, and solid defending after the break.
Schalke may not have managed a maximum haul, but they received a timely boost with attacker Julian Draxler returning from an ankle injury that has sidelined him since December in the second half.
In a tepid opening, it was the visitors who created the best chances with Stefan Bell heading wide from a corner, before Ralf Fahrmann was on hand to parry Elkin Soto's stinging drive for a corner on 18 minutes.
From there Schalke begin to grow into the game and Klaas-Jan Huntelaar had his first sniff at goal on 28 minutes when he forced Loris Karius into a smart save.
Having seen out that attack Mainz went straight up the other end and almost found the breakthrough through Shinji Okazaki who connected well with a cross from the left but side-footed volley was denied by Fahrmann's agile save.
Okazaki had a shot blocked after a marauding run five minutes before the break, while Jefferson Farfan almost finished the best move of the match only for his close-range shot to be deflected wide.
Leon Goretzka almost made a perfect start to the second half for Schalke when his strong effort from inside the box forced Karius into action, before the goalkeeper stood up well to deny Meyer who had capitalised on a mistake in the Mainz defence.
Marius was proving the busier of the two goalkeepers in the second half, and saved Bell's header on the line on the hour mark.
Shortly after Draxler made his return from the bench for Meyer, as Schalke continued to press for the winner.
And they came close in the closing stages, but Boateng wasted a great opportunity when he headed wide in the area with Marius rooted to the spot.
The draw sees Schalke retain their grasp on fourth spot, while Mainz remain seventh.
