Noni Madueke headed the leaders in front on the hour mark, but the Bees were well worthy of at least a point and levelled through Keane Lewis-Potter.
Arsenal’s lead at the top of the table now stands at four points as they aim for a first league title in 22 years.
But Mikel Arteta’s men still have to travel to second-placed City in the remaining 12 games of the season.
A point boosted Brentford’s bid to qualify for European football for the first time as they remain in seventh.
Keith Andrews’ side have only been beaten twice at home all season and Arsenal can count themselves fortunate not to have suffered just a fourth league defeat of the campaign.
David Raya foiled his former club with a stunning save to claw away Igor Thiago’s powerful header with the best chance of the first half.
Arsenal were missing William Saliba and Kai Havertz through illness and injury respectively, but were boosted by the return of Martin Odegaard and Bukayo Saka on the bench.
Arteta sent for Odegaard at half-time to turn the tide and the visitors started the second period with far more intent.
Arsenal’s pressure had its reward when Madueke rose highest at the back post to head Piero Hincapie’s cross back across Caoimhin Kelleher.
However, the visitors were guilty of trying to hold onto their advantage rather than continuing to take the game to Brentford.
Thiago stung the palms of Raya once more as the home side grew in confidence.
Lewis Potter should have levelled earlier when he headed wide from a corner when completely unmarked.
Arsenal’s strength from set-pieces has played a huge role in putting them into pole position for the title.
But they struggled to cope with Brentford’s own prowess from dead balls.
The equaliser arrived from one of Michael Kayode’s long-throws propellled into the box, Sepp van den Berg won the flick-on, and Lewis Potter stole in ahead of Odegaard to head in.
Brentford were the far more likely winners in the final 20 minutes.
Cristhian Mosquera made a vital last-ditch tackle to deny Thiago.
The Brazilian’s best chance for an 18th Premier League goal of the season came in stoppage time but he smashed inches over.
But Arsenal also had a chance to snatch victory at the death when Kelleher raced off his line to save from Gabriel Martinelli.
