We report a measurement of the fraction of b quarks produced diffractively in p¯p collisions at s√=1.8 TeV. Diffraction is identified by the absence of particles in a forward pseudorapidity region. From events with an electron of transverse momentum 9.5<20 GeV/ c within the pseudorapidity region |η|<1.1, the ratio of diffractive to total b-quark production rates is found to be Rb¯b=[0.62±0.19(stat)±0.16(syst)]%. This result is comparable in magnitude to corresponding ratios for W and dijet production but significantly lower than expectations based on factorization.