Not in details, at least not all the time. I might form a more or less concrete image while reading a physical description, but usually the characters stay kind of "blurry"/ in silhouette / seen from the back in most scenes - at least when it comes to their facial features. Like others have mentionned, I'm a lot more sensitive to "voices" when I read.

That's true even for characters that are extremely familiar to me, for instance WOT's. I don't have a mental image of the faces of even the main cast. Nyaeneve for instance I see as a short, slender woman, with brown hair, the complexion of someone spending a lot of time outdoors, and a long braid... but in my head her face remains blurry. Occasionally, the writer highlights a specific facial feature, so that bit I'll picture... with the rest remaining blurry.

I very rarely form mental images for characters based off real people I know/know of. A lot of people seem to do that.