Observation of J/ψ production in weak neutral currents in the calorimeter of the CHORUS detector exposed to the CERN SPS wide-band vμ beam is reported. A spectrum-averaged cross section σJ/ψ = (5.8 ± 2.4) × 10-41 cm2 is obtained for 20 GeV [less-than or equal to] Ev [less-than or equal to] 200 GeV. The data is compared with the theoretical model based on the QCD Z-gluon fusion mechanism.