Narrative:

Flight was lax to las. Normal takeoff, cruise and landing. Landed runway 25L las. First officer was PF. Exited the runway at taxiway A6. As we slowed, I took the aircraft for taxi. Tower said air carrier X cross runway 25R, contact ground point one (121.1). As I turned 90 degree to the runway, the first officer saw an airplane on takeoff runway 25R, just about ready to rotate. I stopped the aircraft but went past the hold short lie, but stopped before the runway edge. Called tower supervisor. Reviewed tapes. Tower did clear us to cross with an aircraft on takeoff roll.

Google
 

Original NASA ASRS Text

Title: B737 FLC INITIATE STOP ACTION WHEN BEGINNING TO CROSS LAS RWY 25R AS THEY OBSERVE A B737 ON TKOF ROLL.

Narrative: FLT WAS LAX TO LAS. NORMAL TKOF, CRUISE AND LNDG. LANDED RWY 25L LAS. FO WAS PF. EXITED THE RWY AT TXWY A6. AS WE SLOWED, I TOOK THE ACFT FOR TAXI. TWR SAID ACR X CROSS RWY 25R, CONTACT GND POINT ONE (121.1). AS I TURNED 90 DEG TO THE RWY, THE FO SAW AN AIRPLANE ON TKOF RWY 25R, JUST ABOUT READY TO ROTATE. I STOPPED THE ACFT BUT WENT PAST THE HOLD SHORT LIE, BUT STOPPED BEFORE THE RWY EDGE. CALLED TWR SUPVR. REVIEWED TAPES. TWR DID CLR US TO CROSS WITH AN ACFT ON TKOF ROLL.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.