I'm editing my answer (again).
Originally I thought this board might be a variation of:
BEC COMPUTER ENTERPRISE 80486AT (Ver. 1.0)
Everything except the position of the BIOS and the TAG seemed to match, but that could have been errors in the diagram.
However, I am now thinking this is a better match:
KOUWELL ELECTRONIC CORPORATION 486-33EZ
As near as I can tell, everything on this diagram matches the pictures from the OP, with two exceptions. First, there is a bank of dip switches labeled SW1 on the diagram but this switch is labeled SW2 and shaped differently in the OP's picture. Second, there is a (I think) battery displayed in the corner of the board on the diagram, but no such battery exists in the OP's picture (but the silkscreen in the OP's picture looks like there was space/connections for the battery) (if it is a battery).
I'm not ignoring the great detective work by Igor, but the Genoa board in his answer doesn't seem to match the physical layout of the OP's picture. However the BEC board is close, and the KOUWELL board is really close.