  The blue supergiant (BSG) problem, namely, the overabundance of BSGs
inconsistent with classical stellar evolution theory, remains an open question
in stellar astrophysics. Several theoretical explanations have been proposed,
which may be tested by their predictions for the characteristic time
variability. In this work, we analyze the light curves of a sample of 20 BSGs
obtained from the Transiting Exoplanet Survey Satellite (TESS) mission. We
report a characteristic signal in the low-frequency
($f\lesssim2\;\mathrm{day}^{-1}$) range for all our targets. The amplitude
spectrum has a peak frequency at $\sim0.2\;\mathrm{day}^{-1}$, and we are able
to fit it by a modified Lorentzian profile. The signal itself shows strong
stochasticity across different TESS sectors, suggesting its driving mechanism
happens on short ($\lesssim\mathrm{months}$) timescales. Our signals resemble
those obtained for a limited sample of hotter OB stars and yellow supergiants,
suggesting their possible common origins. We discuss three possible physical
explanations: stellar winds launched by rotation, convection motions that reach
the stellar surface, and waves from the deep stellar interior. The peak
frequency of the signal favors processes related to the convective zone caused
by the iron opacity peak, and the shape of the spectra might be explained by
the propagation of high-order, damped gravity waves excited from that zone. We
discuss the uncertainties and limitations of all these scenarios.
