High- and low-dispersion optical spectra of the giant H II region CM 67 near the center of the edge-on galaxy NGC 4631 have been obtained. Comparisons are made with radio observations to suggest the existence of a large bar in NGC 4631. Region CM 67 is shown to coincide in position with the easternmost peak of a triple radio-continuum source. It also corresponds very closely with a giant molecular cloud in the CO position-velocity diagram. It is concluded that the optical, nonthermal radio continuum, and CO line emission originate from the same volume of gas. The H II region is typical of high excitation objects, with a ratio (forbidden O III line/H-beta) = 2.8 + or - 0.11 normally found in H II regions located at large galactocentric distances. It is suggested that CM 67 represents the tip of a bar which has a length of several kpc. 35 refs.