There are some, but they aren't as common in Belgium as the Netherlands.
http://www.fietsenwerk.be/nl/welkom-18.htm has some information about bicycle facilities in French or Flemish. I haven't tried google translate on it, but if it doesn't work, you can select that text, and translate that directly.
This page has general parking information
http://www.fietsenwerk.be/nl/diensten-8 ... service=61Unfortunately it doesn't always say what type of parking is available. This site
http://www.mobielbrussel.irisnet.be/art ... modaliteit also has some information.
Two or maybe 3 of Brussels' train stations have guarded cycle parking. Information about them is available from the Belgian Rail site (in English)
http://www.belgianrail.be/en/stations-a ... ation.aspx I'm not sure about Antwerp, but I would expect at least the central station to to have it.
The phrase to google is 'bewaakte fietsenstalling' plus your location of interest. Maybe Dutch speakers on here can make other suggestions.