It depends

I spent a while reading about this, and what appears to be the situation is that lolicon that can be defined as obscene is technically illegal. Read the actual text of the PROTECT Act, whatever websites you'll find searching on google tend to be bad sources of information. There was similar legislation that was struck down by the supreme court, but not this latest one, which differs from the earlier legislation by including the "obscene" definition. There's only been a couple cases that I've found of someone in the US actually getting a sentence for lolicon, usually when people discuss those cases on GC or on the web, they come to the mistaken conclusion that these people were also found to have real CP, or commit some other more serious crime, and that the lolicon was not really the issue. In fact, this is not the case, and they would have been given a sentence simply for the lolicon if that was all that was found. A document summarizing one of the proceedings stated this as well (it discussed the case, I think it was a guide on prosecution for CP-related crimes). Another misconception is that only images that are indistinguishable from photographs (i.e., computer-generated images) are illegal. This is not true, as that section is separate from the one that discusses lolicon ("drawings", etc.).

So in conclusion, if it was found to be obscene (which it probably would - one of the cases I mentioned, I think 16 images were found and all were judged to be obscene) then yes, it would be illegal. But, like I mentioned, there have only been a couple cases since 2003, when the act was passed, and I haven't seen any evidence that the FBI is actively going after people or websites for hosting/possessing/etc. lolicon. So I would consider it to be very low risk.