You need an appropriate undergrad degree, generally, which wouldn't just be a BEng for an MS program. It'd actually be weird to require a BEng for an MS, as that'd exclude all BS and some BA degree holders (if the degree were appropriate, like math is often offered as a BA in the US).
If it's a professional degree (often a terminal degree, not intended to go on to a PhD program) then they often have laxer requirements with respect to the undergraduate degree (basically: have one, have a good enough GPA, and have an appropriate professional background or other training to substitute for the lack of an appropriate undergrad degree).
And then there are schools that basically just admit everyone because they don't care about graduation rates and want that sweet, sweet tuition money.
