We present a direct measurement of the mass difference between top and antitop quarks ($\ensuremath{\Delta}m$) in $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ $t\overline{t}$ final states using the ``matrix element'' method. The purity of the $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ sample is enhanced for $t\overline{t}$ events by identifying at least one of the jets as originating from a $b$ quark. The analyzed data correspond to $3.6\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$ acquired by D0 in Run II of the Fermilab Tevatron Collider. The combination of the $e+\mathrm{\text{jets}}$ and $\ensuremath{\mu}+\mathrm{\text{jets}}$ channels yields $\ensuremath{\Delta}m=0.8\ifmmode\pm\else\textpm\fi{}1.8(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.5(\mathrm{syst})\text{ }\text{ }\mathrm{GeV}$, which is in agreement with the standard model expectation of no mass difference.