I found the answer:
public void async_post(){
//do a twiiter search with a http post
String url = "http://search.twitter.com/search.json";
Map<String, Object> params = new HashMap<String, Object>();
params.put("q", "androidquery");
aq.ajax(url, params, JSONObject.class, new AjaxCallback<JSONObject>() {
@Override
public void callback(String url, JSONObject json, AjaxStatus status) {
showResult(json);
}
});
}