Yes, unless you are in one of the top two KrisFlyer elite member tiers. For everyone else, KrisFlyer miles expire on the last day of the month, 36 months after the month in which they were credited to your miles account. The oldest miles are used first when you redeem them, so you just need to ensure that you redeem miles – for flights, seat upgrades or merchandise – at least once every three years. Your KrisFlyer account page at the Singapore Airlines website, or on your mobile app, will show how many of your miles are due to expire each month for the next six months.
An alternative option is to pay a fee (currently $US12 per 10,000 expiring miles) to extend their validity for six months (12 months for higher status members), or sacrifice 1,200 miles per 10,000 expiring miles to receive the same extension. You could also consider transferring the points to another air miles membership (such as Virgin Australia’s Velocity) if you have one that accepts KrisFlyer miles as a conversion option.