See the biblatex manual, § 2.3.2:
2.3.2 Missing and Omissible Data
The fields marked as ‘required’ in § 2.1.1 are not strictly
required in all cases. The bibliography styles which ship with
this package can get by with as little as a title field for most
entry types. A book published anonymously, a periodical without
an explicit editor, or a software manual without an explicit
author should pose no problem as far as the bibliography is
concerned. Citation styles, however, may have different
requirements. For example, an author-year citation scheme obviously requires an author/editor and a year field.
You may generally use the label field to provide a substitute for
any missing data required for citations. How the label field is
employed depends on the citation style. The author-year
citation styles which come with this package use the label field
as a fallback if either the author/editor or the year is
missing. The numeric styles, on the other hand, do not use it at
all since the numeric scheme is independent of the available
data. The author-title styles ignore it as well, be- cause the
bare title is usually suƿcient to form a unique citation and a
title is expected to be available in any case. The label field
may also be used to override the non-numeric portion of the
automatically generated labelalpha field used by alphabetic
citation styles. See § 4.2.4 for details.
So, depending on the citation style you choose, you might just go with something like this:
@online{question64352,
title = {Citing a Web Page with no author},
url = {http://tex.stackexchange.com/questions/64352/citing-a-web-page-with-no-author},
urldate = {2012-07-23}}