The researches at the NICA accelerator complex (JINR, Joint Institute for Nuclear Research, Dubna) require efficient and fast software implementations of algorithms for modeling and reconstruction of the particle collision events. BmnRoot package developed for the BM@N experiment is based on the ROOT environment, Geant4 and the FairRoot object-oriented framework. BmnRoot includes tools for event simulation, reconstruction and data analysis modules. With the announcement of Geant4MT multithreading support in ROOT and FairRoot, the problem of modifying the BmnRoot code for multithreading simulation appeared. As a result, an event-driven parallelism model has been implemented for event simulation in BmnRoot. The stages of the performed work and the results of testing the implemented multithreaded version are presented.