Sometimes Dell updates or SupportAssist may not be able to install BIOS and give you this error.  Since you didn't provide the model number.  Please go to   [URL] Enter your service Tag > Drivers and Download > BIOS  Now open MSCONFIG > Services > Uncheck Dell updates. Reboot  Run the downloaded BIOS files it will install and reboot Enable Dell updates again from MSCONFIG and open it, (a reboot may be required)  check for updates and it won't show that BIOS update any more.   
Title pretty much says it. Have latest version of Dell Update: 4.1.0. Always says restart is required to complete BIOS update no matter how many times I restart.
Dell Update always says restart required no matter number of times I restart