If it's a POST/BIOS launch, means "all good" hardware detected that is critical for boot. (one beep)
Now, if you are receiving beeps further along into Windows, then there is an issue that needs addressed.
First, consult your Mobo manual, if you have it, or visit your Mobo's manuf. site to obtain a (usually PDF) copy, to see the different beep combos and what they mean.
I am only guessing here, might be a temp or fan failure warning beep you are hearing.
Are your temps fine? (CPU, ambient, Gfx card)
Are all fans spinning while the PC is turned on? Are all fans clean of dust or debris?
Check these areas first, if it persists, and these aren't found to be "wanting" then post more info on brand/model of system, CPU, Mobo, RAM etc