B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 198; Flight Crew Type 9600
Confusion; Distraction; Training / Qualification
Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Person / Animal / Bird
Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Procedure
Gate at ZZZ. At start of second engine; radar began to scan.  Discovered radar switch was left in radar.   I remember glancing at radar selector switch.  It was to the left of center.  But; both radar and standby are left of center.  At some point I remember thinking it's a -700; no need to turn the selector to standby.  I did not recheck the switch to verify that the switch actually was pointed to standby.  I started to check the weather radar and stopped for some reason. After the weather radar started to scan; I saw that the switch was in radar and not test.  The question is; was the switch in radar or did I automatically turn the switch when I was going to test the radar?  The result is the same.  I am responsible either way. People were in and out of the forward area for short periods of time.  The person who I saw the most was the female ramp individual. I estimate that she was at the left 70-90 degrees from the nose of the aircraft at between 20 feet to 25 feet from the aircraft.  Perhaps; five minutes at that position.  Then she operated the tug.  Approximately five minutes from pushback to discovery of the radar switch.  That will be the first switch I check upon entering the flight deck on every single flight.
During the B737-700's second engine start at the gate; the Captain noticed the radar begin scanning and selected standby; but was puzzled whether it had been left ON from the previous flight or his preflight was incomplete.