For a live sample please click here or see below the snippet

<!DOCTYPE html>
<html>
<head>
<title>HTML5 Drawing Arc Between Two Points using Canvas</title>
<script language="javascript">
function DrawArc()
{
	var drawingCanvas = document.getElementById('sampleCanvas');
	if(drawingCanvas.getContext)
	{

		var context = drawingCanvas.getContext('2d');
		context.clearRect(0,0,600,600);
		context.beginPath();
		context.moveTo(30,30);
		context.lineTo(200,30);
		context.arcTo(400,30,400,800,100);//left 1,top 1,left 2,top 2,radius
		context.lineTo(400,400);
		context.stroke();
		//context.fill();
	}
}
</script>
</head>
<body>
<canvas id="sampleCanvas" width="600" height="600" style="border:1px solid #000000">
<p>Your browser doesn't support canvas.</p>
</canvas>
<script>
DrawArc();
</script>

</body>
</html>