The Germany midfielder Ozil moved to the Emirates from Real Madrid for a club record £42.4m fee on transfer deadline day.
Arber wrote on his Twitter feed: "Lovely bit of 14-1 Mesut."
An Arsenal spokesman said: "All our employees and workers are well aware of their responsibilities in this respect and we are looking into this as a matter of urgency."
The FA regulations state: "You are not allowed to place a bet on a game or competition in which you have any influence, either direct or indirect.
"The above includes all bets related to the following: Any other events involving your club or other clubs playing in the same league competition (such as next manager markets)."
@greenbeetle, That's not the point, Mark Arber could have found out Mesut had signed the contract before before placing the bet. I think i read a story that one of the Real Madrid players said he knew Mesut was heading to Arsenal before deadline day so the deal could have already been in place subject to the arrival of Gareth Bale. Real Madrid and Barcelona are clubs that buy all the best talent so who would have thought Arsenal had a chance of signing a world class player like Mesut Ozil for £42 Million when it's usually them selling all their best players.- dannyjohnson