let a=0;
let r=200;
let x=0;
let y=0;
function setup() {
createCanvas(600,600);
}
function draw() {
a++;
x=cos(radians(a))*r+300;
y=sin(radians(a))*r+200;
rect (x,y,100,100,);
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.1.9/p5.min.js"></script>