The *A is the newer version of the *. For some chips there might even be a *B version.
In most cases you will be able to use the *A chip instead of the *, but you'd better check the document that describes the differences. Go to the page on Microchips website that describes the chip, and get the 'migration' document.
Watch out: the 16F87*A chips use a programming algorithm that is very different from the 16F87* chips, so unless your programmer / PC software explcitly supports the 16F87*A chips you will probably not be able to program them.