Scott McDonald's goal six minutes from the end denied 10-man Barnsley a victory at the Riverside.
On-loan Blackpool striker Marlon Harewood put Barnsley ahead after 22 minutes with a close-range finish.
Tykes defender Paul McShane was then sent off for violent conduct in the second half as Boro searched for an equaliser.
It duly arrived through Australian striker McDonald, who headed home a Tarmo Kink cross.
Very few chances were created in the opening exchanges.
Rhys Williams fired a 30-yard drive wide for the home side, but that was as close as either team came early on.
Barnsley made the breakthrough midway through the first half.
The Middlesbrough defence failed to clear Kieran Trippier's corner and, when the ball fell to Harewood in the six-yard box, the former West Ham and Aston Villa striker steered into the bottom corner.
On-loan Chelsea midfielder Jacob Mellis came close to doubling Barnsley's advantage, only for MacDonald to block his effort on the line.
Boro defender Joe Bennett curled a free-kick just wide before Harewood was denied a second goal, his effort well saved by home goalkeeper Paul Smith.
Some strong defending from Barnsley kept the home attack at bay, with Jason Shackell blocking shots from Barry Robson and then Andrew Taylor.
With McShane dismissed with 20 minutes remaining, Middlesbrough pushed hard for an equaliser in the closing stages.
Substitute Kink sent an inviting cross into the area and McDonald nodded his 11th goal of the season past Barnsley goalkeeper Luke Steele to rescue a point for his side.