Harper has enjoyed a prolonged spell in goal for Newcastle in the early weeks of this season, with first-choice keeper Tim Krul suffering an elbow injury on international duty.
Krul is close to a comeback ahead of next week's derby against Sunderland but Harper believes that he has done enough to merit holding onto his spot.
He told the Evening Chronicle: "I would like to get to 300, but I cannot see it happening at my age, but 200 would be nice. That is a landmark I would like to get to.
"Tim's comeback is not too far away, but we do have a lot of games coming up. We've got a long season ahead of us and we know there are plenty of games ahead."
The 37-year-old has played 196 times for the Magpies in 15 seasons of loyal service at St. James' Park.