Yep, draw a box and give it a border radius that is half the width of the box:
#circle {
background: #f00;
width: 200px;
height: 200px;
border-radius: 50%;
}
Working demo:
http://jsfiddle.net/DsW9h/1/
#circle {
background: #f00;
width: 200px;
height: 200px;
border-radius: 50%;
}
<div id="circle"></div>