of course.
you can read about it in the pgfmanual in chapter 39.7:

\usepackage[tikz]
\usetikzlibrary[shapes.callout]

\starttext
\starttikzpicture
    \node[ellips callout, draw] {Hallo!};
\stoptikzpicture
\stoptext

using the options callout relative pointer=(coordinate) and callout absolute pointer=(coordinate), you can modify where it points to, using standard node options you can modify other aspects (positioning, padding, width, height, color, line thickness, …)

beware: i have not tested above code, but it should be obvious.

Philipp