electrical system fails but engine keeps on running

My 2004 CRV has 195.000 trouble free miles. Last month while driving in town, all the electrical system went off, like when you turn the ignition key off, except that the engine kept on running. After pulling over and turning the engine off, it started right back and the whole car electrical system was on again. Now,a month later without any problems, has done it again. All power off but engine keeps on running. My mechanic is buffled . Honda dealer : “never heard of such thing”… Any help would be greatly appretiated