The first is that he's playing PG and has to handle the ball a lot more than anyone else on the team right now. Combined with his minutes, that's generally going to give you more TO's just because of the amount of time with the ball and the probability of a player of his skill level losing it (although this point doesn't account for other PG's who average way fewer TO's).
Second, he's just started to play a ridiculous amount of minutes over the past week and hasn't had enough time to refine himself yet. Did you watch the first couple weeks of games this season? Because of the lockout this year, there were almost no preseason games and it showed. Turnover rates were extremely high for pretty much every team, so I'm inclined to think that Lin can get his turnovers down throughout the rest of the season assuming they keep playing him.
My last point is a pretty obvious one, but he's still young. A few more years of experience and I expect to see turnovers go down. I watched his 38 point game last night, and while he played pretty amazing, he did have moments where he looked confused and flustered when running the offense.