sudo dmidecode -s bios-version

sudo dmidecode | less

BIOS Information
    Vendor: American Megatrends Inc.
    Version: 0309
    Release Date: 04/18/2013
    Address: 0xF0000
    Runtime Size: 64 kB
    ROM Size: 8192 kB
    Characteristics:
        PCI is supported
        APM is supported
        BIOS is upgradeable
        BIOS shadowing is allowed
        Boot from CD is supported
        Selectable boot is supported
        BIOS ROM is socketed
        EDD is supported
        5.25"/1.2 MB floppy services are supported (int 13h)
        3.5"/720 kB floppy services are supported (int 13h)
        3.5"/2.88 MB floppy services are supported (int 13h)
        Print screen service is supported (int 5h)
        8042 keyboard services are supported (int 9h)
        Serial services are supported (int 14h)
        Printer services are supported (int 17h)
        ACPI is supported
        USB legacy is supported
        BIOS boot specification is supported
        Targeted content distribution is supported
        UEFI is supported
    BIOS Revision: 4.6