Some antivirus are sensitive to anything that looks like a crypto miner since there's malware out there that install miners on users' PCs without their consent.

It's always a good practice to run anything crypto-related in a VM or a dedicated rig just to be safe, but at this point I think it's safe to say there's no malware in the Biblepay client. There's always a risk that any website could be compromised, so if you don't want to risk downloading the precompiled binaries you can always compile from source.