Slow-starting McLaren dramatically slashed the gap to Aston Martin since the summer break thanks to an impressive string of podiums over the past four races, while the Silverstone-based squad has generally struggled since the summer.
Norris' latest runner-up spot in last weekend's US Grand Prix was enough for McLaren to leapfrog Aston Martin and hold fourth by six points.
Norris said he was puzzled by how Aston was making its car "slower and slower" in recent weeks and thinks McLaren can still target Ferrari, which is 80 points clear in third.
"It's our target," he said about Ferrari's lead. "I think we're in a good rhythm.
"It's been clear that Aston… I don't know, they seem to have managed to make the car slower and slower with every upgrade that they’ve bought.
"They were racing [Red Bull] at the beginning of the year and they were out in Q1 and then they've been struggling, so I don't know what their issues are."
Aston's Fernando Alonso took six podiums in the first seven grands prix but has only managed to add one top-three finish - second place in the Dutch GP, since then.
Source: Autosport