The 25-year-old has been a standout performer under Roberto De Zerbi in his breakthrough season with the Seagulls, who are targeting European qualification for the first time in their history.
Just four days after scoring for Japan in a 2-1 friendly defeat against Colombia during the international break, Mitoma found the net for Brighton midway through the first half to cancel out Brentford's 10th-minute opener scored by Pontus Jansson.
Mitoma - who has been linked with a host of top European clubs ahead of the summer transfer window - ran in behind the Bees backline and placed a first-time lofted finish over the top of David Raya after receiving a long ball from goalkeeper Jason Steele.
Brentford regained the lead just a minute later through Ivan Toney, though, before a header from Danny Welbeck restored parity for the Seagulls just before the half-hour mark.
Four minutes after the break, Ethan Pinnock put Brentford ahead for a third time, but they were pegged back yet again as Alexis Mac Allister calmy slotted home a 90th-minute equaliser from the penalty spot to rescue a point for Brighton.
Mitoma's first-half strike has increased his goal tally in the Premier League to seven for the season, and in doing so has become the highest-scoring Japanese player in a single Premier League campaign.
The Brighton winger has moved ahead of compatriots Shinji Okazaki and Shinji Kagawa, who both scored six goals in a single Premier League campaign for Leicester City (2017-18) and Manchester United (2012-13) respectively.
Four of Mitoma's seven top-flight goals have been scored at the Amex, with his latest strike against Brentford following home goals against Arsenal, Bournemouth and West Ham United.
The 15-cap Japan international was also on target in away fixtures against Wolverhampton Wanderers, Everton and Leicester City, with Brighton winning on all three occasions.
Brighton's draw with Brentford see them remain in sixth place in the Premier League table, moving to within four points of fifth-placed Newcastle United.
The Seagulls will now prepare for three successive top-flight away games, with a trip to Bournemouth on Tuesday followed by visits to London to face Tottenham Hotspur and Chelsea.