We　calculate　the　geometric　phase　for　an　atomic　qubit　coupled　to　a　zero-temperature　bosonic　reservoir　with　a　Lorentzian　spectral　density.　The　geometric　phase　is　obtained　without　tracing　out　the　degrees　of　freedom　of　the　reservoir.　It　is　shown　that　the　phase　accumulated　by　the　total　system　is　purely　geometric　and　exhibits　an　oscillation　behaviour　in　both　the　Markovian　and　non-Markovian　regimes.