A source at the taping says Simpson dodged the pregnancy question on the show as well, saying that if all the rumors about her were true, she "would have had a baby by now."
The newly-engaged singer also told MTV News, " I just think it's an inappropriate question to ask any woman. For me, that's something that I didn't ever want to respond to, because I think it's an inappropriate question."
Simpson, however, did not put the rumors to rest. "Some things, you want to keep personal, and I think that when people deny [pregnancy reports], it's probably because it's something they want to keep personal."
The TRL appearance is Simpson's first public outing since announcing she and Pete Wentz, 28, got engaged last week. The show will air Thursday.
Just before performing her song "Little Miss Obsessive," Simpson took a question from a female fan, who asked the singer to show off her ring. Simpson, dressed in a black cardigan, white ruffled shirt and tight denim skirt, happily flashed her diamond eternity band that she has had for some time.
Earlier in the day, when asked about her engagement ring while at JFK airport, Simpson told Extra: "It's getting sized. You'll see it soon. It's pretty."
She would not elaborate on how Wentz asked for her hand, telling MTV, "That's all so sacred, I need to keep that to myself."
Simpson, 23, is promoting her new album Bittersweet World, due out April 22. She is also scheduled to perform on the Today show Friday.