Australian teammate Oscar Piastri, 24 points behind the Briton with three rounds remaining going into the weekend's Las Vegas Grand Prix, is also fully focused and ready to fight for the title.
"Oscar's definitely fighting back," Brown told Reuters. "I think one of his greatest strengths is he just gets in the zone. And I've never seen Lando in a better place.
"The booing would have bothered him in the past (but) he recognises that was as much probably booing for me and how we're treating it (the duel between teammates). So he's in a great place. It's not bothering him."
"And the best part is, it's real, right?," added the American, who spent the weekend with both drivers seeing partners and playing golf in San Francisco's Bay Area.
"Sometimes you can go 'don't let that stuff bother you' but you can see it does. He (Norris) is just in a good place, he's doing his thing... he's just engaged, in the zone, totally focused but they're both relaxed. They're not faking it. They're chilled."
Norris bood in Mexico and Brazil
Norris has won the last two races in Mexico and Brazil, and beaten Piastri in the last six, but faced boos from the crowd when he stepped on the podium.
There have been several theories on why -- from fans of Mexican Sergio Perez still allegedly unhappy about some comments by Norris last year, or from others who see McLaren favouring the Briton over Piastri.
Brown also suggested an element of people rooting for the underdog -- now Red Bull's four-time world champion Max Verstappen, as well as Ferrari's Lewis Hamilton and Charles Leclerc.
"I think it's just the nature of the beast," said the boss, whose first book 'Seven Tenths of a Second' -- an autobiography with plenty of business advice -- is published this week.
"I'm getting more social media hate today having won two constructors' (titles) and with first and second in the championship than when we were 17th and 18th.
"You just got to learn that it's actually a small group of keyboard warriors. So we're just staying true to our racing principles."
The weekend could have the championship battle whittled down to just the two McLaren drivers if the gap between Verstappen and Norris balloons from the current 49 points to 58.
That would mean McLaren, who have already clinched the constructors', are sure of taking both titles in the same season for the first time this century.
Brown said his thinking was, as ever, focused more on what could go wrong as much as what might go right.
"My mindset isn't 'Max might be out of the picture'," he explained. "My mindset's a bit 'if we don't have a strong weekend, Max is right back in the game.
"I'd love to be in a position where we leave this race and I know a papaya (McLaren) car is going to be the drivers' champion.
"Last weekend (in Brazil) was great, because Lando extended his lead, but the glass-half-empty side is -- it got closer between Max and Oscar. And what we really want to do is not just win the drivers' championship. We want to finish first and second."