Oh yes it is more than possible. Likely culprits are faulty ground or more likely a polarity mismatch between the gtr amp and the PA. This can also be caused by the amps and PA on different circuits that have uncommon grounds very common in older houses or buildings. Many older music appliances don't have a ground or have had the ground removed or sometimes use non polarized plug or in some cases manufactures used a different wiring scheme.
There are inexpensive electrical outlet testers
that will show ground faults and polatity reversal, I keep one in my gig essential bag, great for diagnosing noise and shock risks.

http://www.acehardware.com/product/index.jsp?productId=2665480&kw=outlet+tester&origkw=outlet+tester&searchId=51914618954

I second the outlet tester...and use it every time we gig a new joint
Happened to one of our old guitar players....same sorta scenario
Was playing an outdoor venue and was singing backup....when he stepped back,the mic hit him on the neck...completing the electrical circuit
He said he was "stuck" and someone else had to free him
Pretty scary stuff....and if I remember correctly,he got a burn on his neck from the experience
Glad it wasn't me
:)
Peace Ed

Thanks for the answer Brad, I'll look into a
tester. I'm guessing either the PA's missing a
ground or the circuits in the house are screwy. Far
as I know the guitar and amp are all pretty new
equipment, not that that rules them out..

Electricity is something we have to understand and respect. Early on I was playing as gig as a thunderstorm hit, everyone took a break and unplugged except a gtr player, lightning struck the pole outside and blew up his tube amp, exploded the tubes, distended the speaker cones, burned the guitar and the players hands. It also set one of the beer coolers on fire. I had a personal lesson from being shocked so badly i had amnesia for 3 days.

Yeah I saw this happen to a soundman! Further investigation found a bad outlet, the ground wire was touching the hot wire this made the outside of the mike 110 volts, waiting for a ground like guitar strings. A cheap tester would be great to throw in your gig bag.

Whenever i am playing a new place I always get there early and test the outlets and mark the bad ones with duct tape or masking tape.