With the Mac mini EFI Firmware Update 1.8 Apple takes issue with USB keyboards targeted. It is aimed at owners of the Mac mini model, which was introduced in late 2012.
In concrete terms, the firmware update (via 9to5Mac) fixed a bug where after you wake up the Mac mini from hibernation a connected USB keyboard is no longer detected.
This update is recommended for Mac mini (late 2012) models. This update addresses an issue that may prevent a USB keyboard from being recognized after the system wakes from sleep.
The only 4.4 MB update can be loaded in the affected Mac minis on the App Store and requires a reboot. The latest generation of Mac mini, which was introduced last year, is not affected by this issue.