The cross section of the process e+e-tomu+mu- was measured in the SND experiment at the VEPP-2M e+e- collider in the energy region sqrt{s}=980, 1040 -- 1380 MeV. The event numbers of the process e+e-tomu+mu- were normalized to the integrated luminosi
ty measured using e+e-to e+e- and e+e-togammagamma processes. The ratio of the measured cross section to the theoretically predicted value is 1.006pm 0.007 pm 0.016 and 1.005 pm 0.007 pm 0.018 in the first and second case respectively. Using results of the measurements, the electromagnetic running coupling constant alpha in the energy region sqrt{s}=1040 -- 1380 MeV was obtained <1/alpha> = 134.1pm 0.5 pm 1.2 and this is in agreement with theoretical expectation.
