We report evidence for direct CP violation in the decay B0→K+π− with 253 fb−1 of data collected with the Belle detector at the KEKB e+e− collider. Using 275×106 B¯¯¯B pairs we observe a B→K±π∓ signal with 2140±53 events. The measured CP violating asymmetry is ACP(K+π−)=−0.101±0.025(stat)±0.005(syst), corresponding to a significance of 3.9σ including systematics. We also search for CP violation in the decays B+→K+π0 and B+→π+π0. The measured CP violating asymmetries are ACP(K+π0)=0.04±0.05(stat)±0.02(syst) and ACP(π+π0)=−0.02±0.10(stat)±0.01(syst), corresponding to the intervals −0.05<ACP(K+π0)<0.13 and −0.18<ACP(π+π0)<0.14 at 90% confidence level.