Barnsley led courtesy of a Jamal Campbell-Ryce header after 46 minutes when Forest failed to clear Bobby Hassell's long throw.
The home side should have wrapped up the points but Campbell-Ryce's second-half penalty was straight at the keeper.
Barnsley's only effort on target in the first half came early on when flying winger Campbell-Ryce showed an impressive burst down the left and cut inside but his raking shot was easy for keeper Iain Turner.
But Forest went close when Nathan Tyson clipped a clever low pass from the left.
Leading scorer Earnshaw should have done better but hoisted his casual effort over the top from close range.
In the 38th minute a surging run by Chris Cohen had the home side in trouble when he shot and Heinz Muller spilled the save but it was cleared.
Barnsley midfielder Hugo Colace speculated with a long-range effort but it dipped over the top from 25 yards.
But many of the fans were still not back in their seats when Barnsley broke the deadlock in the first minute of the second half.
A long throw by Hassell was aimed at Darren Moore. It bounced over him and as Forest dithered, Campbell-Ryce headed a looping effort into the top corner.
But after 51 minutes, Forest could have been level when Earnshaw latched onto a loose ball after a great run by Chris Cohen.
His blistering shot from the edge of the area hit the underside of the bar and was cleared.
Seven minutes later, Barnsley's Andranik Teymourian made a surging run into the area and was cut down by Wes Morgan.
The Iranian midfielder grabbed the ball to take the kick himself but reluctantly handed it over to Campbell-Ryce who messed up the spot-kick and Turner saved easily.
But Earnshaw levelled after 68 minutes with a super ground hugging shot from 15 yards after Isaiah Osbourne's cross from the right to earn his side a precious point.