MK Dons extended their unbeaten run to eight games after Michel Pensee-Bilong's second-half equaliser.
Daniel Nardiello had given Barnsley the lead on the stroke of half-time, after Stephen McPhail's through ball caught the Dons' defence square.
But the Dons levelled when defender Bilong hammered home Dean Lewington's out-swinging free-kick.
Gareth Edds went close three times for the visitors, while McPhail saw his acrobatic volley cleared off the line.
Barnsley: Flinders, Tonge, Hassell, Tom Williams, Robbie Williams, Shuker, Burns, McPhail, Wroe, Nardiello (Boulding 75), Johnson.
Subs Not Used: Scarsella, Jarman, Baker, Laight.
Booked: Robbie Williams.
Goals: Nardiello 45.
Milton Keynes Dons: Baker, Oyedele, Palmer, Pensee-Bilong, Crooks, Kamara (Rizzo 75), Edds, Harding, Lewington, Platt, Small (Puncheon 72).
Subs Not Used: Smart, Smith, Herve.
Goals: Pensee-Bilong 55.
Ref: T Leake (Lancashire).