The acceptable operands for the mov instruction are shown here.
mov [eax], [ebx] is attempting to move one memory location (dereferenced from the value in the ebx register) to the memory location referred to in eax. There is no opcode for mov that takes a memory location as both the source and the destination, but there are opcodes for moving a memory location into a register, a register into a memory location, an immediate to a register, an immediate to a memory location, or a 16-bit GPR into a segment register.
