pop up

verb

To come up with a "pop" sound.
“The toast is in the toaster - when it pops up it will be ready.”
To appear without warning.
“I can't remember where I left my keys, but they normally pop up somewhere.”
“Across Japan, technology companies and private investors are racing to install devices that until recently they had little interest in: solar panels. Massive solar parks are popping up as part of a rapid build-up that one developer likened to an "explosion."”
(Of an alert, advertisement, etc.) To suddenly appear onscreen.
“[…]where you should put the disclaimer for software (somewhere that the user sees it when they start the program, tho' I wouldn't do that, just put it in the 'about' box like the mpgn.com guy suggests -- otherwise, having something pop up makes it annoyware, IMHO).”
To display as an alert, advertisement, etc. that suddenly appears on screen.
“My computer just popped up a warning about Internet security.”