My Scion tc has 140,000 miles on it and today while driving it just started revving to 3 or 4 rpm before actually movement. So I was just wondering if it was or could be the spark plugs?

Sounds like you need to replace your throttle control sensor. And you can check for any vacume leaks to see if any cracked or loose lines , Best of luck to you.

No it is not your plugs, your trans is slipping (not good)-make sure you have trans fluid in it (if it is an automatic) and if it is a stick you are going to need a clutch real soon, drive it gently so you don't have to have it towed (don't let it 'slip' be gentle with the gas petal)-if it is an automatic, and it does not need fluid, same advise,drive it gently, gradually accelerating until you can get it to a trans repair facility, because you won't be able to drive it very long like that.