No. When you installed Avast for the first time, and you've ran the first Smart Scan, at the end of the scan you were asked if you want to run Smart Scan once a month. Maybe you forgotten to uncheck that option, and this is the reason.
If you want to see the scheduled tasks open Avast, go to Protection---Virus Scans----Custom Scans, and see if I was right.
Also, tell me when you installed Avast.