The COMET experiment at J-PARK (Japan) will search for the lepton-flavor violating μ-e conversion process. The MEPhI&ITEP group is responsible for the design and construction of the cosmic anti-coincidence system. It will be based on scintillator strips with WLS fibers and SiPM readout. Detailed simulation work is planned to choose the optimal anti-coincidence system geometry, after which the prototype will be designed and built. Studies of the cosmic rays detection efficiency by multilayer scintillation detectors will be conducted, with a goal to reach an efficiency in excess of 99.99%.