Is there a virus in Sumatra sources?

Some people report that their anti-virus software complains about executables in bin directory of Sumatra sources.

Is there really a virus in them?

No.

False positives are unfortunately quite common in all popular anti-virus programs. You can always verify what your particular anti-virus program says against what other anti-virus programs say by using https://www.virustotal.com/.

If only one or two report a given file as having a virus, it's most likely a false positive.