swarner793 / Scott is absolutely correct, and types faster than I
Here's some additional info you may find useful Sir ...
General comment: depending upon the item for which you make application, you may have to disclose even expunged records.
It has been my experience that many job applications AND several states issuing Non-Resident permits require disclosure of even expunged incidents; sometimes without timeframe, sometimes within a fixed timeframe (examples: anything in the last 5 years, or midemeanors in the last 2 / felonies in the last 7, etc...)
You may also wish to carefully read and intrepret the verbiage used, the question is often not whether or not you were CONVICTED, but whether or not you were ARRESTED ... you may be best served to state YES to the question of whether or not you have been ARRESTED even if the incident was later expunged as a result of an ARD (Accelerated Rehabilitative Disposition) program or as a result of Nolle Prosque, Charges Dropped, Found Not Guilty, etc ...
Also, for many permits, it may diverge, asking for CONVICTIONS, then asking for ARRESTS for select items (examples: Domestic Violence, Stalking). There is often no language on the application stating "Exclude Expunged items" although if you drill down into the application's "fine print" you may find such.
Comment: If you believe it was expunged, better verify it before answering the question. Many ARD programs or similar automatically perform expungement, many others ALLOW expungement after successful completion of the program but you must still APPLY for expungement YOURSELF.
In many cases this is an easy process and does not require an Attorney, for example in Allegheny County the Clerk of Courts Office can assist you in doing so for a modest fee.
Even for expunged items, a record of the ARREST may still come up during a NICS / NCIC check.
For incidents that occurred within PA, the suggetion by previous posters of using the PA PATCH system is an excellent one (for all of us, especially if you have a very common name). In this day and age of identity theft and whatnot, it may even be prudent to "check yourself" occasionally to make certain you are not listed in error.
I had a situation some years past attending a family picnic where a relative of a similar age to me needed a car to run for some charcoal and propane.
(He wasnt drinking, was in his late 20's, drove there but his car was blocked in, I had no reason to assume he had no license but in hindsight should have asked).
Unbeknownst to me, he did not have a license. Ran a stop sign in a County Park, County PD grabbed him, he ID'd himself as ME, since he was only wearing swim trunks and knew my name, address, phone and birthday they cited him using my vehicle registration info. (I later found that the County PD radioed their office and since I was listed in the WHITE PAGES that was verification enough for them...) He was scared and never disclosed the incident to me, I didnt know til I got a hearing notice for failure to respond to the ticket. Took a few months to straighten out, narrowly averting having my license suspended - and this was just a summary citation. Imagine the headache if this had been something far more serious ...
I run myself through PATCH and the Unified Courts system every 4 months at the same time that I make request to one of the credit agencies (rotate thru and do one of the 3 every 4 months) for my free annual credit report. As a UTAH Instructor, I am also run thru NICS once every 24 hrs. Due to my UTAH duties my info is out there on _tons_ of applications (State Instructor stamp includes name and addy, and I must offer my Utah state ID and display a copy of my commission upon request of any student).
Overkill? Nope. Cheap insurance at $30/yr for 3 PATCH searches. You bet.
... hope this helps ...