Is paying off my rental with 3.5% interest rate a good idea?

[Frazz Wick]

I have been renting my first home out for 3 years. The rent I collect 1950/month which is two times the mortgage payment. I only owe $45,000 and I'm considering paying off the house within the next 2 years. 

What are your thoughts here. Is this a good idea? My thought is from a piece of mind perspective. Paying off the house would mean I own it free and clear. I'm conflicted however, because I want to buy another rental soon.