The USA international, who joined the Reds on loan from Orlando City in January, lashed home his third strike goal for the club just four minutes into the second period to seal a seventh consecutive victory.
A vintage performance it was not, though Dyke's fierce effort was worthy of deciding any match and leaves Valerien Ismael's men in the final play-off berth with 12 games left to play.
Harlee Dean should have given the visitors the lead as early as the sixth minute, but directed a free header from Gary Gardner's inviting right-wing free-kick into the turf and wide of the near post when it looked easier to score.
With Barnsley playing far too many hopeful long balls forwards, they struggled to create anything resembling a clear-cut chance at the other end.
Cauley Woodrow did find enough space on the right side of the Birmingham penalty area to drag a low effort across the face of goal, though that was about as good as it got for the hosts during the opening period.
Presumably unimpressed by the disjointed first-half display that his players had served up, Ismael opted to make a double-substitution at the interval, introducing Jordan Williams and Carlton Morris.
And, the change paid off almost immediately with Morris rolling a 49th-minute pass cross-field and setting Dike away down the right.
The on-loan American striker advanced into the penalty area and took aim with his right foot, unleashing a ferocious strike which beat Neil Etheridge at his near post on its way into the roof of the net.
There was little by way of goalmouth action thereafter, though the Blues did come on strong during the closing stages, with Barnsley dropping deeper and deeper as the afternoon wore on.
But, despite them seeing plenty of the ball, City failed to seriously extend home custodian Brad Collins.
The Reds stopper was forced to tip over an 89th-minute header by Jeremie Bela, however the flag was already up for offside.
One last-gasp opportunity would materialise for the visitors to salvage a point, Bela's dangerous cross from the left finding its way through to Ivan Sanchez at the back stick, though the Spaniard scuffed his shot.
Barnsley: Collins; Sollbauer (Sibbick 71), Helik, Andersen; Brittain, Mowatt, Palmer (Halme 58), Styles (Williams 46); Frieser (Morris 46), Woodrow (Adeboyejo 87), Dike. Unused substitutes: Walton, Oduor, Kane, Chaplin.
Birmingham City: Etheridge; Valery, Roberts, Dean, Friend (Sanchez 69), Pedersen; Gardner, Harper (Cosgrove 84), Sunjic; Hogan, Jutkiewicz (Bela 70). Unused substitutes: Prieto, Colin, Clayton, Leko, Clarke-Salter, Halilovic.
Referee: G Scott (Oxfordshire).