I observe similar queries in logs of my web-server too (I have lighttpd+mysql running small forum on top of RT-N16).

Someone is scanning internet looking for admin pages of typical services and other common vulnerabilities exposed to internet. That's pretty common and there's no good way to block them (at least I don't know any).

I wouldn't worry about them unless you found something relevant to your web site (like multiple strange requests to some script).