We present the first search for CPT-violating effects in the mixing of B0s mesons using the full Run II data set with an integrated luminosity of 10.4  fb−1 of proton-antiproton collisions collected using the D0 detector at the Fermilab Tevatron Collider. We measure the CPT-violating asymmetry in the decay B0s→μ±D±s as a function of celestial direction and sidereal phase. We find no evidence for CPT-violating effects and place limits on the direction and magnitude of flavor-dependent CPT- and Lorentz-invariance violating coupling coefficients. We find 95% confidence intervals of Δa⊥<1.2×10−12  GeV and (−0.8<ΔaT−0.396ΔaZ<3.9)×10−13  GeV.