Substitute, Leandro Trossard scored his first goal for Arsenal but the Premier League leaders missed the chance to move eight points clear at the top.
After a goalless first half in which the Bees hit the woodwork through Toney, the Gunners took the lead when Trossard slot in a Bukayo Saka pass at the back post four minutes after coming off the bench.
Brentford got the reward for their excellent performance at Emirates Stadium when Toney nodded in Christian Norgaard’s cross from close range.
Arsenal raised the tempo in the closing stages – including seven minutes of added time – as they searched for a winner but Brentford completed an excellent defensive display by holding firm for a point.
Arsenal face Manchester City – six points behind before their game on Sunday afternoon against Aston Villa – in a top-of-the table showdown on 15 February.
Brentford, meanwhile, are eighth and just five points off fifth placed, Tottenham who lost to Iheanacho inspired Leicester.
