Public Performance of downloaded scores from musescore

Yes, if it is Public Domain. Else you need the copyright holder's permission.

The answer to the question is identical whether you got the scores from musescore.com, from any other website, by purchasing sheet music at a store, or just learned the song by ear. That is, musescore.com plays no role in whether you can perform a song publicly or not.

If the song is public domain in your country (generally, more than 100 years old, but it's not that simple) you can always perform publicly.

If it's not public domain, then it's more complicated. In the US, you can generally perform most copyrighted material in any venue that has a "blanket license" from a performing rights society - most clubs, bars, & restaurants that have live music do this and you'll see ASCAP, BMI, and SESAC stickers in the window making this clear. other countries may have similar setups.

For more information on this, you'd need to do more research into the copyright laws in your particular country, but again - none of it has anything to do with MuseScore. Where you get the sheet music from has no bearing on whether or not it's legal to perform it publicly.