I agree with the others to have your oil pressure checked (with a
mechanical gage).  But I doubt if the problem is truly low oil pressure
(but you don't want to assume that and damage your engine).

On a properly operating engine, your oil pressure will be at its
absolute lowest when running when the engine is at operating
temperature, idling, in gear, and vehicle stopped.  With a good oil
pressure switch, this will be above the trip point of the switch with
some margin.  If the pressure switch is out of calibration (due to an
internal leak), then normal idle may not trigger it (the pressure would
be just above the incorrect trip point with no margin), but if the idle
drops just a tad below normal (SAY, WHEN THERE IS A VACUUM CHANGE DUE TO
APPLYING THE BRAKES), then it will trip the switch and light the dash light.

If you are traveling down the road in gear, does the light come on?  Or
is it only when you are stopped, in gear, with the brakes on?  If the
pressure switch is bad, the latter will be the case.

My advice: Get the pressure checked as others suggested, and while they
have the switch out to temporarily hook up the mechanical gage, heve
them put in a new switch - OEM only - not aftermarket.  The switch
itself will cost less than $30.

My full expectation if you do that is that (1) You will verify that your
pressure is in spec., and (2) The light problem will be gone.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')